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The chemical structure largely influences the composition and distribution of pyrolysis products. Investigating the objective rules of structural characteristics and pyrolysis reactions of oil sands bitumen can enhance the knowledge of the pyrolysis reaction mechanism. This paper carried out the extensive experimental characterization of the chemical structure of Karamay oil sands bitumen (KBS) in Xinjiang, China. Then, the thermal evolution mechanism of the chemical structure of KBS was investigated by focusing on the thermogravimetric analysis and combining the characterization results of KBS at different pyrolysis final temperatures. The results show that the pyrolysis of KBS belonged to a parallel reaction. On one hand, aliphatic groups, as the main structure, undergo thermal cracking reactions to produce light oil. The oxygen-containing functional groups contributed to the production of CO and CO 2. On the other hand, the aromatic structure, which has a high degree of condensation and high tightness, would condense into a more challenging to decompose coke during pyrolysis. Meanwhile, pyridinic was condensed into quaternary at this stage. The hydroxyl group in the oxygen-containing functional group structure was present in the coke due to its better thermal stability. Finally, the paper proposed the pyrolysis reaction path for the chemical structure of KBS. • Chinese oil sands bitumen chemical structure was characterized. • Pyrolysis of Karamay oil sands bitumen belonged to a parallel reaction. • The aliphatic structure produces oil while the aromatics produce coke. • Pyridine and pyrrole undergo a condensation reaction during the pyrolysis inversion. • Proposed a pyrolysis reaction path for the chemical structure of Karamay bitumen. [ABSTRACT FROM AUTHOR]

In the brackish water sedimentary environment of the Junggar Basin in Xinjiang, the organic-rich shale and shale oil formation with relatively low maturity, is characterized by relatively high abundance of C 28 regular steranes. However, the biogenic source of organic matter and favorable sedimentary environment for the type of source rock has been thoroughly classified. In this paper, organic geochemical and petrological, analyses of the Lucaogou Formation shale in the Jimusaer Sag, Junggar Basin in the north of Xinjiang Uygur Autonomy Region were carried out. The source rocks in the Lucaogou Formation are mainly composed of two types of maceral including lamalginite (cyanobacteria) and telalginite (green algae), with the former predominantly fueling the high C 28 regular sterane content. Petrological, organic and inorganic geochemical analyses suggest that the lamalginite was developed in low-salinity water while the telalginite was developed in high-salinity water. Based on geochemical and organic petrological characteristics, both the lamalginite and telalginite have good hydrocarbon-generating potential, but in the lower thermal evolution stage of the Lucaogou Formation source rock, telalginite have higher hydrocarbon-generating rate. • Lamalginite (cyanobacteria) is the primary source of C 28 regular steranes. • The lamalginite (cyanobacteria) is more developed when the salinity is low and the telalginite (green algae) is more developed when the salinity is high. • In the lower thermal evolution stage of the Lucaogou Formation source rock, the lamalginite (cyanobacteria) has lower hydrocarbon-generating rate than the telalginite (green algae). [ABSTRACT FROM AUTHOR]

Wellbore failure is the most headache and common problem in drilling engineering. Wireline loggings like caliper log and image log are usually used to identify wellbore failure. However, it is impossible to discern the failure types and take steps in real-time using the post-drilling methods. During the drilling process, various cavings will circulate to the ground with drilling fluid when wellbore instability occurs. These cavings are the foremost indicator of wellbore deterioration and have a potential link to the mechanism of borehole failure. Unfortunately, the use of cavings to understand borehole instability and its mechanism requires correct descriptions of caving which are inclined to be qualitative and fragmentary in previous studies, as well as proper interpretation which entails a wealth of field experience and comprehensive understanding of drilling, geo-mechanics and geology. This paper proposes a new method for caving characterization and a caving interpretation workflow based on image processing and machine learning. Firstly, we thoroughly analyze all modes of borehole failures and the corresponding cavings they generate, and make clear the significant characteristics to distinguish different types of cavings. Then the morphologies of caving contour and surface are quantitatively characterized using Speeded-Up Robust Features (SURF) algorithm and 2D- Discrete Wavelet Transform (DWT), respectively. These two categories of characteristics are used as the input of Light Gradient Boosting Machine (LightGBM)-based classification model, and the mode of borehole failure that generates the caving can be inferred from the classification results. We demonstrate the application of this interpretation workflow utilizing the cavings from the T oilfield, Xinjiang, China. The result shows that the average accuracy of classification is 90.9 %, which reflects that the workflow has a satisfactory performance in caving interpretation as well as that the features have high representativeness and robustness for caving characterization. This method opens up a new path to the early warning of borehole instability and real-time diagnosis of instability mechanism, thus corresponding remedies can be taken in time to avoid serious downhole accidents. • The differences of morphology between various types of cavings are summarized into two aspects: contour and surface. • Contour morphology is quantitatively characterized based on the SURF algorithm. • 2D-DWT is applied to extract the characteristics of surface morphology at multi scales. • A caving interpretation model that links the morphology of caving to the mode of borehole instability is built. [ABSTRACT FROM AUTHOR]

There are only a few related studies focused on the steam assisted gravity drainage (SAGD) dilation start-up technology (termed as dilation start-up in this paper), especially with true triaxial stress physical modelling experiments in the laboratory. Therefore, in order to better understand the dilation start-up process, four large-scale (1050 mm × 410 mm × 410 mm) true triaxial experiments of SAGD start-up with dual horizontal wells were conducted for the first time by using the oil sands from the Xinjiang oilfield, northwest China. The dilation process characterized by temperature changes at different positions inside the experimental samples was monitored in real time. The performance differences between dilation start-up and conventional start-up were discussed in detail, and the effects of dilation pressure and dilation time on the dilation process were also studied. The experimental results indicate that dilation start-up can significantly reduce the well communication time between injector and producer, and enhance the range of dilation zone and improve the uniformity of dilation zone along the horizontal wellbores. Moreover, we find that dilation pressure is an essential factor influencing the dilation effect. The average communication parameter increases by 5% if dilation pressure increases by 10% whereas the standard deviation of communication parameter decreases. The evolution of dilation zone with time shows that long-time dilation prompts the uniform propagation of dilation zone along the horizontal wellbores. This study provides guidance for the optimization of SAGD dilation start-up in shallow heavy oil reservoirs. • Four large-scale true triaxial experiments of SAGD start-up with dual horizontal wells were conducted. • Dilation process characterized by temperature changes inside the samples was monitored in real time. • Effects of dilation pressure and dilation time on the SAGD dilation start-up were studied. [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]