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The Jurassic Badaowan formation of the tight oil reservoir in northwest Xinjiang, China, is featured by a complex in situ stress pattern, leading to an unclear understanding of the orientation and geometry of a propagated hydraulic fracture. In this regard, a three-dimensional (3-D) in situ stress field was first configured based on a detailed mechanical earth model of the region of concern. Secondly, a fluid-solid-damage coupling model was established to explore the influences of the in situ stresses and the engineering parameters on fracture propagation. Finally, a systematic approach was proposed to characterize the updated stress field and the fracture morphology reconfigured by the in situ stress. The findings disclose that the reservoir is mainly controlled by reverse faults that generate horizontal fractures in most parts of the region. The in situ stress follows the strike-slip fault pattern where vertical fractures are dominant in the central and southeastern part of the reservoir, where the vertical fracture tends to be constrained in the oil layer when the interlayer minimum stress difference ∆Sh becomes greater than 4 MPa in the southeast. In addition, as the injection rate increases, the width of a fracture increases, whereas its height decreases. The viscosity has negligible effect on the fracture height, but its increase can enlarge the fracture width and decrease the length. Here, the cross-dipole shear wave logging record in a field well was used to verify the proposed method, showing that the predicted fracture morphology was consistent with the field test result. The research can aid field engineers in predicting fracture morphology for optimizing a fracturing scheme. [ABSTRACT FROM AUTHOR]

It is challenging to enhance heavy oil recovery in the late stages of steam flooding. This challenge is due to reduced residual oil saturation, high steam-oil ratio, and lower profitability. A field test of the CO2-assisted steam flooding technique was carried out in the steam-flooded heavy oil reservoir in the J6 block of the Xinjiang oil field (China). In the field test, a positive response to the CO2-assisted steam flooding treatment was observed, including a gradually increasing heavy oil production, an increase in the formation pressure, and a decrease in the water cut. The production wells in the test area mainly exhibited four types of production dynamics, and some of the production wells exhibited production dynamics that were completely different from those during steam flooding. After being flooded via CO2-assisted steam flooding, these wells exhibited a gravity drainage pattern without steam channeling issues, and hence, they yielded stable oil production. In addition, emulsified oil and CO2 foam were produced from the production well, which agreed well with the results of laboratory-scale tests. The reservoir-simulation-based prediction for the test reservoir shows that the CO2-assisted steam flooding technique can reduce the steam-oil ratio from 12 m3 (CWE)/t to 6 m3 (CWE)/t and can yield a final recovery factor of 70%. [ABSTRACT FROM AUTHOR]

• The super-heavy oil reservoir with interlayers were classified quantitatively by geological and producing parameters. • New way was given for evaluating the development effects of SAGD during the mid-later stages in super heavy oil reservoirs. • Fuzzy comprehensive evaluation method and analytic hierarchy processes were introduced firstly to the evaluating processes. • New standards the ranking of five producing parameters were determinated based on influences for developments effects. The problems of energy consumption and decreasing production are prominent during the middle and later stages of steam-assisted gravity drainage (SAGD) in super-heavy oil reservoirs. Geological parameters and production parameters have an important impact on the development effects. However, there is no quantitative method to evaluate production effects of SAGD during the middle and later stages. In order to fill this gap, this study proposed a new approach to quantitatively evaluate the development effects of SAGD by considering the geological and production parameters for super-heavy reservoirs. Where, the primary factors controlling reservoir's characteristics and development effects of SAGD were determined by using numerical simulation method. There are 42 well pairs that have already entered the middle and later stages using SAGD in the Xinjiang oil field, China, which were taken as an example. Firstly, a fuzzy cluster analysis model was established to classify reservoir by considering three geological indicators. The results indicated the potential of production for each well pair. Then a fuzzy comprehensive evaluation model was established to evaluate development effects by considering five production indicators. The new standards and ranking of evaluation indicators were quantitatively confirmed by using analytic hierarchy processes. Finally, the approach combined reservoirs classification and development effects evaluation to provide a quantitative and comprehensive evaluation of each well pair. The oil recovery ratio and utilization degree of the horizontal section can clearly reflect the development effects according to comprehensive evaluation results, which means that when the well group meets the recovery factor less than 3.0% and the utilization degree of horizontal section less than 85.0%, the development effects are evaluated as "Category III". Based on the evaluation results, the corresponding follow-up adjustment measures can be adopted. This study has guidance on the development of technical countermeasures for different types of well pairs. [ABSTRACT FROM AUTHOR]

Steam-assisted gravity drainage (SAGD) methods have been widely applied in oil-sands exploitation globally. SAGD processes are effective only after thermal and hydraulic communication between the injector and producer has been established during the start-up operation of the well pair. The geomechanical SAGD dilation startup has been considered a promising technology that can enhance permeabilities of heavy-oil reservoirs and reduce thermal conformance time. However, limited studies have focused on the practical operational procedures of geomechanical SAGD dilation startup. This paper presents the application of SAGD dilation startup technology in a shallow super heavy-oil reservoir in the Karamay oil field, China. The general reservoir geology and geomechanical characteristics were investigated and used to propose a practical approach to determine dilation initiation pressure. We also summarize the SAGD well completions and geomechanical SAGD dilation startup procedures. A case study using a real SAGD well is presented and analyzed. We then share the field operation procedures and results after dilation startup. The objective of the research was to reduce the steam circulation time and achieve uniform thermal conformance along the SAGD well. Our field results highlight the promising potential of using water injection to create a dilated zone and dramatically enhance reservoir permeability. The performance of SAGD dilation startup in the Karamay oil field is evaluated by comparing the cumulative oil production rate with those from SAGD wells using conventional startup. • The geomechanical properties of Karamay heavy oil reservoirs are characterized. • A practical approach to determine dilation initiation pressure for SAGD startup is proposed. • A field case study of geomechanical SAGD dilation startup is presented and analyzed. [ABSTRACT FROM AUTHOR]