Recently, 15.1 billion tons of shale oil geological resources were discovered in the Qingshankou Formation of Gulong Sag, Songliao Basin, and this discovery has attracted considerable attention. Thus far, the sedimentary environment and diagenetic process of the Qingshankou Formation in Gulong Sag, particularly the reservoir space and accumulation mechanism of the shale oil, are unclear, which has seriously affected the exploration and development of shale oil. Based on detailed core and thin section observation, thin section analysis, mineral analysis, and geochemical analysis, thin layers and concretions of dolostone in Qingshankou Formation shale in Gulong Sag are studied. Three types of layers and nodules can be seen in the core and thin sections: the first is composed of very pure micrite, powdery calcite, or dolomite (dolomite greater than 90%); the second are argillaceous dolomite thin layers or nodules (dolomite content of approximately 75–90%); and the third is a highly impure dolomite thin layer (dolomite content between 50–75%). The chemical composition of three kinds of dolomite thin layers and nodules is different: the contents of CaO and MgO of the pure dolomite thin layer and nodules are more than 40%. The contents of CaO and MgO in the thin layer and nodules of argillaceous dolomite are between 30 and 40%. The content of CaO and MgO in the impure dolomite thin layers and nodules is less than 30%. The reservoir space is developed at the micron or nanometer scale in the thin dolomite layers and nodules, although most of these layers are filled with asphalt. The development of thin layers and nodules of dolomites is related to a dry and hot depositional climate and influenced by hydrothermal fluids. The findings presented here provide important information for exploiting the newly discovered shale oil resources. Many dolostone thin layers and nodules have curved silt veins, and the bending coefficient is 1.48, indicating that the dolostone thin layers and nodules have undergone compaction after formation.
Previously, stratigraphic evolution and sequence overlapping were represented by "substituting point for surface or multi-point for surface, line for surface or multi-line for surface", making it difficult to accurately reflect the stratigraphic evolution law across a larger area. We investigate the application of the seismic horizontal slice method for medium-short term stratigraphic sequence (four level), divided into reservoir group received, based on a 450 km 2 study area of three-dimensional (3D) seismic fine of the Sa-Pu formations west of the Daqing placanticline using a 50-millisecond horizontal slice. Sa-Pu oil layers can be divided into seven four-level sequences. We believe that a four-level sequence is more accurate in this application than in logging and data logging.
Development of unconventional resources has become major focus in China in the recent years as the growth of energy demands. Many pilot projects on shale oil reservoirs have been initiated to seek for economic development with modern hydraulic fracturing technologies. Fracturing these reservoirs is quite challenging and requires not only large reservoir contacts but also high fracture conductivity in both primary fracture and fracture networks since oil viscosity is several magnitudes higher than natural gas. Vertical fracture connectivity is also an issue in many cases due to lamination of shale-rich layers with thin siliceous and calcareous beds. This typical sedimentary feature may result in either short fracture height or pinch-point in vertical fracture profile due to proppant embedment in shale-rich layers.The paper presents a shale oil case study in Northern Songliao Basin in China in which many fracturing treatments have been attempted in the past without success. Two existing vertical wells drilled in 1989 were used to study appreciate fracturing techniques and demonstrate the possibility of economic production before evaluating horizontal well completion. The paper illustrates optimization of treatment strategy and design by integrating detailed reservoir characterization, fracture simulation using unconventional fracture model and numerical reservoir simulations. It also introduces an innovative fiber diversion technique for improved vertical fracture coverage and proppant placement together with real time fracture monitoring for treatment optimization.After increased understanding from the treatment on the first well, the treatment on the second well was quite successful and the well produces 30 bopd after the treatment, which is the first ever economic production in the field. The first month production history also matches with the forecast very well, which increases the confidence of extending the practice to the entire field as well as subsequent horizontal well evaluation. TX 75083-3836, U.S.A., fax +1-972-952-9435
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