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In recent years, tight sandstone gas as one of the important types of unconventional resources, has been rapid explored and developed. There are large-scale tight sandstone gas production in Sichuan Basin, Ordos Basin, Bohai Bay Basin, Songliao Basin and other basins, and it has become a key part in the area of increasing gas reserves and production in China. Due to the influence of the reservoir characteristics, tight gas reservoirs have low porosity and permeability, and the tight gas can only be effectively developed by improving the conductivity around the wellbore. Therefore, it is required to perform hydraulic fracturing after the completion of horizontal well drilling to improve the permeability of reservoir. It can be seen that hydraulic fracturing is the core technology for efficient development of tight gas resources. The implementation of hydraulic fracturing scheme directly determines the horizontal well production and EUR. This paper describes the workflow of 3D geomechanical modeling, technical application for Well YQ 3-3-H4 reservoir stimulation treatment, and carries out hydraulic fracture propagation simulation research based on 3D geomechanical model. This paper also compares the micro-seismic data with the simulation results, and the comparison results show that the propagation model is consistent with the micro-seismic monitoring data, which verifies the accuracy of the model. This paper clarifies the distribution law of hydraulic fractures in the three-dimensional space of horizontal wells in YQ 3 block, and the research results can be used to provide guidance and suggestions for the optimization of fracturing design of horizontal wells in tight gas of Sichuan Basin.

How to realize the efficient development of tight oil reservoir is a key and difficult problem for the unconventional resources of China. To realize the effective development of tight oil reservoir, it is necessary to the reservoir stimulation technology to improve the seepage capacity of low permeability reservoirs and increase the productivity of wells. Reservoir geomechanics is one of the main factors affecting hydraulic fracturing effect. Domestic and foreign experts have conducted a large number of studies on the characteristics of reservoir geomechanics. However, most of them studied the regional geomechanical characteristics based on logging data, lithology characteristics and three-dimensional seismic. Such static geomechanics studies can better reflect the in-situ stress characteristics of reservoirs before hydraulic fracutring but also have limitations and uncertainties in the understanding of regional geomechanical characteristics. Based on the one-dimensional geomechanical study, this paper uses structural characteristics and seismic attributes to study the three-dimensional mechanics spatial distribution characteristics of reservoirs. On this basis, this paper performs dynamic (4D) stress field simulation combined with real-time fracturing treatment and microseismic monitoring data. The research results can be used to guide the design of horizontal wells fracturing design and provide strong technical support for the production capacity construction. This paper studies the static and dynamic geomechanics of Baikou Quan Formation in Da 13 block, Junggar Basin and describes the research methods and processes and applies them to the design and optimization of reservoir stimulation schemes. The research results can help reduce operational costs and improve the efficiency of measures and serves as technical support for the efficient development of tight reservoirs in China.

Fault stability refers to the risk level of reactivation of the pre-existing fault in the stress field. Fault reactivation within the oilfield is mainly caused by the increase of fluid pressure in the fault zone. The quantitative evaluation index of the fault stability is the critical fluid pressure (that is, additional fluid pressure) required for fault reactivation under the current pore fluid pressure. When the formation pore pressure reaches the critical value, the corresponding fault part will be in the critical stress state. The sliding of the fault in the critical stress state will easily cause oil and gas leakage and casing damage at the edge of the fault. Therefore, it is of great significance to study fault stability for oilfield production. Ground stress is a key parameter for fault stability evaluation. There are many methods to calculate the geomechanics including hydraulic method, acoustic emission method, and the use of the logging data, among which the hydraulic fracturing method can be used to obtain the most accurate horizontal minimum principal stress. This paper calculates the continuous geomechanics by using the logging data. There are many methods available for evaluating fault stability, among which fault sealing analysis technology (FAST) method is most widely used. FAST can be used to not only quantitatively evaluate fault stability, but also evaluate the impact of fault cohesion on fault stability. There are many factors affecting fault stability. The relationship between the differential stress and tensile strength of the fault rock will affect the trend of the fault reactivation.The direction of the stress field also affects the fault stability greatly. The argillaceous material weakens the strength of fault rock. When a large amount of argillaceous material enters the fault zone, the fault tends to reactivate. The change of reservoir fluid pressure will also lead to the change of horizontal stress to affect the stability of the fault. In addition, the accuracy of seismic interpretation will also affect the evaluation results of fault stability. Based on the geological model framework and one-dimensional geomechanical model calibration, this paper establishes a three-dimensional geomechanical model by using the finite element simulation method to carry out four-dimensional geomechanical research to evaluate the fault stability in the development of the Donghe 1 Reservoir in Tarim basin. The research results show that the fracture sealing gradually strengthens during the development of Donghe 1 Reservoir, and the quantized critical fracture opening pressure is 67.38MPa.

Reservoir pressure and pore pressure coefficient are the key parameters for evaluating the preservation conditions of low permeability reservoirs and selecting different development processed and measures, as well as important input parameters for predicting ground stress. Due to the influence of unique geological characteristics such as ancient structure, current structure and rapid change of burial depth, the pore pressure in reservoir of the Upper Wuerhe Formation in the 53 east block of Junggar Basin has a large lateral change and is influenced by many factors. The conventional pore pressure prediction methods based on longitudinal wave velocity (such as Eaton method) have poor accuracy. Therefore, according to the geological characteristics of the reservoir in this area, based on the simultaneous inversion of P-wave and S-wave data before seismic stack, combined with the changes in formation lithology and the impact of denudation on pore pressure and pore pressure coefficient, this paper takes P-wave, S-wave, lithology, and denudation into account to predict pore pressure and pressure coefficient. The research results show that: ① the introduction of seismic inversion data improves the prediction accuracy and detail richness on the plane; ② the introduction of the lithology change factor improves the stability of the prediction of pressure coefficient in vertical direction; ③ for the area suffering from strong denudation, the introduction of denudation intensity help better predict the pressure coefficient of low pressure wells near the denudated area. The pressure data from more than 10 actual wells proves that the relative error of the prediction results of this method is less than 5%. It is concluded that the established prediction method has small error and high accuracy, and can be used to provide higher quality data support for the subsequent selection of good reservoirs, well location deployment, horizontal stress parameter prediction.

Low-permeability gas reservoirs generally have the lowproduction, production rapid productivity decline, and low-ultimate recovery. Staged fracturing is usually conducted for horizontal wells. Hydraulic fracturing technology isgenerally used to improve fracture conductivity and well productivity. How to accurately characterize and simulate the distribution characteristics of hydraulic fracture network in 3D space is particularly important. The stress interference between hydraulic fractures as the objective mechanical behavior in the process of staged fracturing affects the geometry fracture network and the productivity of the reservoir post-fracturing. The hydraulic fractures simulation in natural fractured reservoirs is complex shapes, mainly because natural fractures affect the propagation path of hydraulic fractures. The theoretical model used to describe the hydraulic fracturing in homogeneous reservoirs cannot accurately show the complexity of the spatial morphology of hydraulic fractures in naturally fractured formations. The operatorurgently needs a mechanical model that can show the stress interference behavior between multiple fractures and the direction of hydraulic fracture propagation, and be used to simulate the spatial form of multiple hydraulic fractures in staged fracturing of horizontal wells and their propagation behavior in naturally fractured formations. Aiming at the impact of natural fractures in the reservoir on the propagation path of hydraulic fractures, this paper established a mechanical model for distinguishing interference behavior of natural fractures and hydraulic fractures. And analyzed the stress field at the tip of the hydraulic fracture and the stress field acting on the natural fracture surface based on the theories related to rock mechanics and fracture mechanics. On the basis of coupling the 3D geomechanical model and the 3D Discrete Fracture Network (DFN) model, this paper established the discriminant model for hydraulic fractures penetrating natural fractures in 3D space to conduct hydraulic fracture propagation simulation for the horizontal well. The research results can be used to optimize the hydraulic fracturing treatment design,and provide technical support for the effective production and profitable development of low-permeability reservoir resources.

Junggar Basin is a typical superimposed oil and gas bearing basin in western China, where Mahu Depression is the largest oil-gas accumulation zone and exploration area. On April 23rd, 2013, the peak daily oil production of Mahu No.1 well reached 52 tons, achieving a significant breakthrough. On August 23rd of the same year, the high yield of Mahu No.18 well opened a new chapter of oil and gas exploration in the slope belt of the Mahu Depression. Since then, CNPC (China National Petroleum Corporation) has increased the exploration and development process of the Mahu Depression, establishing the exploration theory and technology system of the conglomerate reservoir in the depression area. Finally, the exploration and discovery of a supergiant conglomerate oil field (1 billion tons) were achieved. However, a series of development problems were exposed, which was due to the lack of in-depth research on reservoir geomechanics and distribution law for natural fractures: 1) The Hydraulic fracture propagation law is not clear; 2) In the process of fracturing, there exists an obvious phenomenon of non-uniform fluid inflow and expansion in various clusters of fractures; 3) Serious interference occurs between wells during the fracturing operation. Therefore, it is necessary to strengthen the study of geomechanics and distribution law for natural fractures in unconventional oil reservoirs, so as to provide technical support for the optimization of the horizontal well fracturing scheme, improvement of well pattern deployment parameters, and adjustment of oil reservoir development scheme, which further leads to cost reduction and development efficiency improvement while increasing single well production in unconventional oil reservoirs.

A tight oil reservoir is characterized by developed natural fractures, strong heterogeneity, and anisotropy. During long-term production, the geomechanical parameters change accordingly, which results in the difference in hydraulic complex fracture propagation between the infill well and the parent well. The difference is the key factor for infill well placement and hydraulic fracturing treatment. In this paper, a numerical modeling method was proposed to investigate the infill well complex fractures propagation based on four-dimensional stress evolution during parent wells production. This method integrates with heterogeneity and anisotropy of geomechanical parameters and natural fractures, as well as the flow-geomechanics coupling process during parent wells production. The field data, including well-test data, fracturing injection data, and numerical simulation data, were involved in verifying the method. A modelling case of the Da13 region in the Junggar Basin tight oil reservoir was involved in studying the four-dimensional in-situ stress evolution and its impact on the propagation law of infill well complex fractures propagation. It can be drawn from the result that all the principal stresses decrease after long-term production, but the stress difference increases. The increase of stress difference is the largest in the region nearby the wellbore. On the basis of the 3D geomechanical modeling, with the consideration of the stress shadow, proppant settlement, and migration, the full 3D coupling simulation of artificial fractures was realized to provide support for the numerical simulation of the post-horizontal well pressure productivity. Based on the actual segmentation of Well Da 136_ H, additional productivity numerical simulation was conducted for seven segment length schemes. The EUR of the 10-year single well ranged from 25100 to 44200 tons. Case 8 provides the best development effect. However, when the fracturing segment length is less than 75 meters, the EUR increases little, and the fracturing cost increases significantly. The recommended single fracturing segment length is 75 meters.

Low-permeability oil reservoirs generally have the low production, production rapid productivity decline, and low-ultimate recovery. Staged fracturing is usually conducted for horizontal wells. Hydraulic fracturing technology is generally used to improve fracture conductivity and well productivity, which is one of the key technologies for Enhance Oil Recovery (EOR). How to accurately characterize and simulate the distribution characteristics of hydraulic fracture network in 3D space is particularly important. The stress interference between hydraulic fractures as the objective mechanical behavior in the process of staged fracturing affects the geometry fracture network and the productivity of the reservoir post-fracturing. The hydraulic fractures simulation in natural fractured reservoirs is complex shapes, mainly because natural fractures affect the propagation path of hydraulic fractures. The theoretical model used to describe the hydraulic fracturing in homogeneous reservoirs cannot accurately show the complexity of the spatial morphology of hydraulic fractures in naturally fractured formations. CNCP (the operator) urgently need a mechanical model that can show the stress interference behavior between multiple fractures and the direction of hydraulic fracture propagation, and be used to simulate the spatial form of multiple hydraulic fractures in staged fracturing of horizontal wells and their propagation behavior in naturally fractured formations. Aiming at the impact of natural fractures in the reservoir on the propagation path of hydraulic fractures, this paper established a mechanical model for distinguishing interference behavior of natural fractures and hydraulic fractures. And analyzed the stress field at the tip of the hydraulic fracture and the stress field acting on the natural fracture surface based on the theories related to rock mechanics and fracture mechanics. On the basis of coupling the 3D geomechanical model and the 3D Discrete Fracture Network (DFN) model, this paper established the discriminant model for hydraulic fractures penetrating natural fractures in 3D space to conduct hydraulic fracture propagation simulation for the horizontal well. The research results can be used to optimize the hydraulic fracturing treatment design, and provide technical support for the effective production and profitable development of low-permeability reservoir resources.

Fault stability is the risk of reactivation under dynamic stress conditions. The reactivation of faults in the oilfield is mainly caused by the increase of fluid pressure in the reservoir zone, with the quantitative evaluation index of the critical reservoir pressure required for fault reactivation under the current pore pressure condition. When the formation pore pressure reaches the critical stress, the corresponding fault part will be in a critical stress state. The slippage of the critical stress fault tends to cause fluids leakage. Therefore, the study of fault stability is of great significance to oilfield production; In order to guarantee national natural gas peak regulation and supply, the YH underground gas storage (UGS) has been proposed and is carried out with the project of expanding storage capacity and increasing production. The operator hopes to effectively guide the optimization of the limit operation pressure and ensure its long-term safe operation. It is urgently required to carry out fault stability evaluation for the YH underground gas storage. The operator plans to find out the conditions for the activation of the faults, with studies about the stability of the fault under the impact of mining and the impact of the system parameters on the stability of the fault. The results suggest that: whether the fault is in a stable or active state depends on the magnitude relationship between the apparent friction factor (k1) and the fault friction factor (k). When k1 < k, the fault will be in a self-locking state. However, when k1 ≥ k, the fault is in a reactive state. The apparent friction factor reflects the stress risk level of the fault under the collective impact of the in situ stress (including σ1 and σ3), the cohesion of the fault plane (c) and fluid pressure of fault (pi). Higher k1 indicates higher tendency of fault re-activation. k is a quantity factor determined by the friction angle (φ) within the fault. The larger friction angle of fault indicates higher friction factor and the more stable state. The system parameters (includingφ, c, pi, σ1 and σ3) will affect the stability of the fault after the change of initial stress conditions: the smaller cohesion of the fault plane and greater fracture fluid pressure indicate the fault will be easier to reactivate. This paper established the 4D dynamic geomechanical model of the YH underground gas storage and took the fault stability as the judgement basis to analyze the in-situ stress characteristics of different faults. The research results could be used to evaluate the UGS operation safety quantitatively under the impact of the dynamic stress conditions, which will provide technical guidance for optimizing the operation plan of the UGS.

Shale gas reservoirs are characterized in low gas abundance, poor permeability, lower natural productivity than the lower limit of industrial oil flow, and rapid formation energy decline. At present, the technology of horizontal well drilling and staged hydraulic fracturing is widely used for the exploitation of such low-porosity and low-permeability reservoirs. The long well section of the horizontal well in the reservoir and the hydraulic fractures formed by fracturing act as the "underground expressway" for the deep gas in the reservoir to flow toward the wellbore. Their combination can greatly increase the production performance of the oil and gas resources in the reservoir. Staged multi-cluster fracturing in horizontal wells is the key technology to achieve the profitable shale gas production. The results of on-site downhole perforation imaging and distributed optical fiber temperature and acoustic monitoring show that there are obvious non-uniform liquid inflow and expansion phenomena in each cluster of fractures during the fracturing process. Relevant research results also show that factors such as the heterogeneity of the reservoir and the stress interference caused by the propagation of multiple fractures are the main causes of the non-uniform propagation of hydraulic fractures. Therefore, it is accessible to simulate the complex balanced expansion of each cluster of fractures in the fracturing section to improve the coverage of hydraulic fractures in the horizontal well section with numerical simulation methods based on the basic theory of elasticity and fracture mechanics, to reveal how the above engineering geological factors influence and control the fracture propagation. The results of the simulation of the fracturing treatment section of the deep shale gas horizontal well by the fracture propagation model are consistent with the micro-seismic monitoring results,which has obvious significance for accelerating the exploitation of difficult-to-exploit resources and guaranteeing the supply of gas resources.

Since the tight sandstone gas reservoir which is widely distributed in China has become increasingly important in oil field with the further development of resource, it is extraordinarily meaningful for the sustainable and healthy development of China’s energy industry to explore its benefit development mode. Though great achievements have made with the wide use of the hydraulic fracturing technology, which serves as an effective process measure to increase the productivity of a single well, in the development of global unconventional oil and gas resources, there have been many technical problems exposed. A critical one is that if the fractured stage length is too long, the oil and gas resources won’t be effectively exploited, and if it is too short, the operation cost and time will be increased apparently. Therefore, it is urgently required to make plans for determining the optimal length of the fractured reservoir based on different geological features of the oil and gas reservoirs. This paper took the tight oil reservoir in Lower Wuerhe formation in study area as the research case, determined 5 fracturing stage length cases combined with the treatment status and pumping injection procedure of M oil field: Case A (40m), Case B(50m), Case C (60m), Case D (70m) and Case E(80m), and realized fully 3D coupled simulation of the hydraulic fractures in H1 well based on the 3D geomechanical modeling and 3D DFN model with considering multiple factors including stress shadow, proppant settlement and migration using the unstructured grid technology to preprocess it to improve the capacity prediction accuracy of numerical simulation. The productivity prediction results showed that the 10-year EUR (Estimated Ultimate Recovery) of a single well ranged from 35,500 tons to 48,200 tons. With the comprehensive production and fracturing operation cost being considered comprehensively, it was recommended that the optimal length of the single fractured reservoir should be 60 meters.

The unconventional oil and gas resources continuously discovered in China are mainly concentrated in the Junggar Basin, Ordos Basin, Sichuan Basin and Songliao Basin. However, the porosity and permeability of its shale reservoirs are extremely low, which brings relatively great difficulties and challenges to the economic development of shale oil reservoir. Long horizontal well section drilling and multi-stage hydraulic fracturing are the key technologies of unconventional resources development. The operations can increase the stimulated volume and ultimately achieve the goal of improving production. In addition, shale reservoirs natural fractures and horizontal bedding are developed, leading to shear slip and tensile failure during the fracturing propagation process. Moreover, the hydraulic fracture is no longer a single symmetrical two-wing fracture, and it is very likely to form a relatively very complex fracture network. This will bring many inconveniences to shale hydraulic fracturing design, fracture monitoring and interpretation, and post-fracturing productivity prediction. Geomechanics is the important influencing parameter that affects the design of hydraulic fracturing. This research is mainly based on the research results of 3D geomechanics to continuously optimize hydraulic fracturing design for horizontal wells. In addition, the implementation of hydraulic fracturing can significantly reduce the seepage resistance of fluids in the formation near the bottom of the well. This will be a very effective mean to increase well production for unconventional resources. Hydraulic fracturing optimization technique fully-coupling 3D geomechanical modeling was applied in the unconventional reservoir in the northeast of Junggar Basin. The shale oil reservoir of Permian Lucaogou formation is one of the main unconventional resources in China. This case study discusses the multi-stages fracturing optimization of horizontal well-A based on the fully coupled 3D Geomechanical modeling. The research result clearly characterizes the stress model variation and reduces the uncertainties in horizontal well-A1 for hydraulic fracturing operation. The uncertainty of the fracture modeling geometry was greatly reduced, and fracture geometry was verified by micro-seismic patterns. The geomechanical modeling helps to optimize the pressure pumping rate, the volume of proppant and fracturing fluids, eventually maximizes the increase of fracture flow conductivity and post-stimulation production.

In order to ensure the national demand for peak shaving and supply guarantee, the project of Xiangguosi underground gas storage capacity expansion for target productivity has been proposed and being carried out. For the purpose of effectively guiding the optimization of the operation upper limit pressure of the gas storage and ensuring its long-term safe operation, it is urgently needed to carry out the assessment of the integrity of the cap rock of the gas storage and the stability of its faults. Based on geological, seismic, logging, dynamic monitoring data and core experimental data, this paper established static and dynamic geomechanical models of the gas storage and analyzed the characteristics of the in-situ stress of different layers of it to simulate and evaluate the stability of the cap rock, underpinning layer and faults of reservoir under different pore pressure. The results showed that 5 reservoir-controlling faults had no risk of fault activation in the early operation of the gas storage and the current stress conditions, with good sealing performance, and when the reservoir pressure was 6MPa higher than the original formation pressure, there was a risk of instability in the integrity of the gas storage. The research results finely and quantitatively evaluated the operation safety of the gas storage under the influence of the dynamic stress field, and had important guiding significance for the optimization of the operation plan of the gas storage.

The Sichuan shale gas deposits are in remote, mountainous regions and the gas-bearing rocks are deep and in tectonically complicated areas. The plan to make shale gas account for more than 40% of the Chinese total natural gas production by 2040 requires shorter well delivery periods and higher well productions. It is therefore crucial to improve the overall drilling efficiency with the limited rig capability and geological challenges. To improve capital efficiency, a multi-disciplinary approach integrating subsurface understanding with well engineering and drilling practices was implemented. Central to this drilling optimization effort are risk mitigation strategies, utilizing solutions based on robust geomechanical understanding and critical drilling experience reviews, engineered to improve wellbore placement, drilling fluid formulation, and bit and BHA designs. A novel wellbore-strengthening oil-based mud system was implemented to maintain shale stability. A rotary steerable drilling system and reservoir navigation technology were deployed together with the application of specific poly-crystalline diamond compact (PDC) bit design. A new-generation advanced cuttings analysis method was also applied with the lithology, organic matter and fracability of rock could be evaluated in real time to assist the reservoir navigation during the drilling. This integrated solution was deployed in the drilling of 8 ½" holes of Changning Shale gas field. A cross-functional team was formed so that the operator, the drilling contractor and the service company can collaborate closely with expertise across multiple functions and disciplines. Suitable mud weight was provided by the detailed geomechanical analysis to account for the high pore pressure and near bed-parallel drilling conditions. To place the laterals in the thin targeted sub-layer with high TOC, a rotary steerable system (RSS) with azimuthal GR provide not only precise steering and directional controls, but also enable increased reservoir coverage by expanding the lateral section as well as drilling the build and horizontal sections in a single run without BHA trips. The combination of RSS with specialized bits as an optimized bit and BHA system maximizes the steering performance while delivering superior borehole quality by reducing drill string vibration and the minimizing mechanical specific energy, all of which contribute to the overall improvement in the well delivery efficiency. This integrated drilling solution has achieved remarkable results by doubling the average rate of penetration (ROP) to 15.5m/h compared to an offset well on the same pad of 7.4m/h. The well was placed successfully in the targeted zone with a 100% reservoir contact. And the total drilling time was shortened by 40% compared to similar wells nearby. The integrated solution has brought breakthrough to improve the well delivery efficiency in the China shale gas development. This paper describes the integrated workflow solutions and detailed technical optimizations of the 8 ½" section drilling process.

Horizontal well drilling contribute to a dramatic increase of shale gas production in unconventional reservoirs. However, the drilling is also risky and challenging with different types of drilling problems often encountered including stuck pipes, inflows, losses and pack-offs, etc. To reduce shale-gas development costs, shale gas operators are faced with finding effective solutions to minimize drilling risks and improve drilling efficiency. A holistic workflow, which can be divided into three steps: pre-drilled modelling and assessment, real-time monitoring, and post-drilled validation, is proposed. Based on the pre-drilled geomechanical modeling, mud weights, mud formulations and casing setting depths are optimized to ensure wellbore stability during the drilling process. Real-time operations involve monitoring drilling parameters and cavings characteristics (shape and volume), and providing updated recommendations for field drilling engineers to mitigate and reduce borehole instability related problems. During the post-drilled stage, the updated geomechanical model will be used for optimizing the drilling designs of upcoming wells. With geomechanics as foundation, a systematic workflow was developed to provide integrated solutions by using multiple technologies and services to reduce serious wellbore instability caused by abnormal formation pressures, wellbore collapse and other complex drilling problems. The implementation of the systematic and holistic workflow has proven to be extremely successful in supporting the drilling of shale gas wells in China. The integrated approach, which was applied in a Changning shale gas block in Sichuan Basin for the first time in March 2019, recorded an improvement in ROP by 111.2% and a reduction in mud losses by 89.9% compared with an offset well without the risk mitigation strategy applied in the same pad. The geomechanics-based approach provides a convenient and effective means to assist field engineers in mud weight optimization, drilling risk assessments, and horizontal well drilling performance evaluation. The approach can also be extended to reduce potential drilling risks and improve wellbore stability, all of which contributes to reducing drilling costs and optimizing subsequent massive hydraulic fracturing jobs.

Exploration focus is moving into deeper targets of high pressure and high temperature (HPHT) regime due to the ever-increasing energy demand of China. Overpressure and wellbore instability related problems in such setting are mainly associated with narrow drilling margin resulting in severe well control incidents and increased drilling cost. In order to reduce drilling risks and operation costs, an accurate geomechanical model is necessary. The model provides technical support for drilling process and minimum reservoir damage due to optimal mud weight program. Well-scale (1D) Mechanical Earth Model (MEM) is constructed on the offset wells which consist of rock strength properties and stress profile by incorporating all available data including open hole log data, geomechanical core lab results, LOT/FIT, direct pore pressure measurements and drilling events. Furthermore, 3D geomechanics model is generated using available well-scale MEM data in the field and distributed throughout the field which guided by seismic interpretation data as distribution control. The 3D geomechanical model is used to design mud weight and casing program for the upcoming well. The offset wells in the study areas were drilled through complex geological settings with high overpressure (13500 psi) and high temperature (200-220 deg C). Therefore, drilling operations is also risky with different types of drilling events encountered frequently including stuck pipe, inflow, losses and connection gas etc. With 3D geomechanical model as the foundation, the integrated approach helps ultra-deep wells to reduce serious wellbore instability caused by abnormal formation pressure, wellbore collapse and other complex drilling problems. The implementation of systematic and holistic workflow has proven to be extremely successful in supporting the drilling of HPHT wells in China. The integrated solution has been applied in the ultra-deep well, recorded an improvement in ROP by 35.3% and decrease no-productive time (NPT) by 25.3% compared with offset well. The geomechanical approach provides a convenient means to assist field engineers in the optimization of mud weight, risk assessment, and evaluation of HPHT wells drilling performance. The findings will provide reference and guideline for de-risk and performance improvement in HPHT wells drilling.

Drilling operations is risky due to narrow mud weight windows in deep wells. Different type of drilling events and wellbore instability have encountered frequently including inflow, drilling induced tensile fractures (DITF), losses and connection gas etc. As such to mitigate the problems, a robust pore pressure prediction is necessary with requires an understanding of the origins and distribution of overpressures in the area. The technical research process is divided into three steps: pre-drill pore pressure predication (PPP) modelling, real-time monitoring and post-drill validation. Efforts were made to understand the geological settings and temperature model. A pore pressure predication (PPP) model was built by integrating fully coupled geomechanical with thermodynamics modeling. Real-time monitoring information provides references and guidelines for PPP model optimization. During the post-drill stage, the updated PPP model was used to design a mud weight and casing program for the upcoming wells. The study area is located northwestern China, the deep formations that more than 7000 meters are ultra-high temperature (200-220 deg C). Thermal-related secondary pore pressure generating mechanism may become active leading to higher overpressure and difficulties in prediction. For the case study, an empirical relationship of overpressure impact factors versus temperature of sandstone and mudstone was proposed. An accurate PPP model is generated using available well-scale geomechanical model and overpressure impact factors. With an integrating fully coupled PPP model as foundation, the integrated approach helps to reduce serious wellbore instability caused by abnormal formation pressure, wellbore collapse and other complex drilling problems deep wells. A1 well was safely drilled guided by the study result and has no significant wellbore instability issues and has minimum reservoir damage due to optimal mud weight program. These findings will provide reference for overpressure mechanics study of deep wells. The multidisciplinary study results have created value by improving drilling performance and well delivery efficiency. It can also help operator reduce drilling costs and make development plan decisions.

The shale revolution has extended the life cycle of the oil and gas industry, promoted the growth of global oil and gas reserves and production, and changed the energy's strategic pattern of various countries. At present, the national shale-gas demonstration area of PetroChina Changning and Weiyuan is in the stage of large-scale production. Horizontal well and hydraulic fracturing are two key technology that have proven to provide an effective way to economically develop medium to high maturity shale gas resources. However, due to geological complexity of the shale-gas demonstration area, and the lack of robust analysis and research on overpressure mechanism and wellbore instability characteristics, drilling events such as stuck pipes, lost circulations and inflows occurred frequently during horizontal well drilling. These non-productive events greatly restricts the wellbore construction cycle time and the production of shale gas reservoir. A comprehensive geomechanical study was carried out from which the three pressure profiles required for drilling, i.e., pore pressure, collapse pressure and fracture gradient, are established. The study also clarified the spatial distribution of overpressure across the field. The improved pore pressure and geomechanical understanding of the field provides the necessary inputs for an integrated, multi-disciplinary approach carried out during pre-drilled analyses, real-time monitoring and post-drilled evaluation to manage the stability of horizontal wells. The safe mud weight window derived from geomechanics provides the basis for mud weight and mud formulation designs that can be continuously optimized to improve wellbore stability and reduce drilling risks. The integrated approach has been applied for 4 horizontal wells in Weiyuan's shale gas field. One of the wells, Wei202-H34-3, has the horizontal section length of 2500m, making it the longest horizontal section recorded in the block. Drilling performance analyses of the well showed that the overall drilling risk, the wellbore construction time, and the drilling costs were substantially reduced by optimizing the drilling operations through geomechanics integrations and applications. The experience and knowledge obtained from this integrated workflow will provide guidance and serve as reference for the efficient development of unconventional oil and gas reservoirs in China.