Study On Formation And Distribution Of The Shale Reservoir In The Lower Third Member Of Eogene Shahejie Formation In Luojia Area Of Zhanhua Sag

The exploration and development of unconventional oil and gas resources arebecoming increasingly important with conventional oil and gas resources graduallydecreasing, in which shale oil and gas resources have broad prospects for explorationbecause of the huge potential. Zhanhua Sag is one of the most developed areas ofshale hydrocarbon reservoirs in Jiyang Depression, which mainly generates oil, and sofar several prospecting wells have produced commercial oil flow in Zhanhua Sag, butpeople have done very little research on the formation law of the shale reservoir andlack effective evaluation methods. So it is essential to study on shale petrologiccharacteristics, reservoir features in shale, and various factors that affect the shalereservoir. Then one method of evaluating shale reservoir should be established topredict favorable areas which can offer a great help for the further exploration andresearch.In the paper, on the basis of core observation, thin section identification, andscanning electron microscopic analyses, combined with a variety of laboratory datasuch as X-diffraction, organic geochemical testing and so on, the shale in the lowerthird member of Shahejie Formation in the study area should be divided into4majorcategories and7types, which are laminated bondstone, laminated marl, massive marl,laminated calcareous shale, massive calcareous mudstone, silty mudstone, andmassive mudstone. There are mainly there kinds of pores and four kinds of fracturesin the shale. Pores include organic matter pores, recrystallized intercrystal pores andclay mineral intercrystal pores; fractures involve structural fractures, abnormalpressure fractures, mineral shrinkage fratures and interlaminar fractures. The factorsthat affect the development of the shale reservoir consist of lithology and mineralcomposition, content and occurrence of organic matter, tectogenesis and diagenesis.Lithology has a significant influence on the shale reservoir. By the analysis ofreservoir space types and their relative content developed in different kinds oflithology, the shale reservoir can be qualitatively divided into there categories: thebest reservoir includes laminated bondstone, laminated marl and laminated calcareousshale; the second-best reservoir includes massive marl and massive mudstone; theworst reservoir includes massive calcareous mudstone and silty mudstone. Studies show that there is a positive correlation between the density of structural fractures andthe content of calcite; mineral shrinkage fratures mainly exist in the clay mineral;interlaminar fractures are dominately developed in the laminated shale. TOC of theshale in the study area is high, mostly1%-4%, which is beneficial to produce fractures.The occurrence of organic matter also plays an important role on the oil and gasreservoir and migration. There are three main occurrences, which include dence andlaterally continuous layers (mode A), sparse and laterally continuous layers (mode B),sparse and laterally discontinuous layers (mode C). Tectogenesis contributes a lot toproduce structural fractures. Generally the closer away from the fault, the moreintensively structural fractures develop. Diagenesis plays a certain role on improvingthe shale reservoir. The shale is in the middle diagenetic stage A, in which claymineral transformation, generation of hydrocarbon and recrystallization have a greaterimpact on the shale reservoir.Finally, the four factors that affect the shale reservoir are integrated to predictfavorable areas. The low-stand system tract in the sequence1is the best layer toexplore, in which the reservoir space is most developed and the lithology of laminatedbondstone is the best exploration target.