| Sichuan basin is one of oil-gas-bearing basins in our country, where northeast Sichuanarea as significant oil-producing areas plays an important role in oil and gas reservesof Sichuan. Especially Huanglong formation in Carbonic is important exploration anddevelopment layer in northeast Sichuan which contributes to production largely. Thispaper has summarized formation mechanism of good reservoir through analysis ofsedimentary facies of reservoir, rock type, reservoir space type, reservoir geochemicalcharacteristics response and crack characters, all of which offer foundation for oil-gasexploration in Huanglong formation of northeast Sichuan.According to comprehensive study of sedimentology, lithology, sedimentarygeochemical, reservoir geology and mathematical geology, on the basis of that,combine with logging geology, seismic geology and geochemical data, this paper getsthree creation points from analysis of sedimentary face character, plane evolution oflithofacies paleogeography, reservoir geochemical response, reservoir space type andcrack characters.(1)Through detailed research on sedimentary face, sub-face and micro-face, thispaper makes certain that Carbonic Huanglong formation belong to sabakha and theGulf shelf sedimentary circumstance, and build shore beach-sabakha-Gulf shelfsedimentary model. On the basis of that, plane distribution map of sedimentarymicro-facies in three section of Huanglong formation are carried out with analysis ofregional tectonic background, then discuss geometric shape, plane distribution andevolution regular in different sedimentary facies belts of every lithologic intervaldeeply,and their relationship with reservoir development.(2) The Huanglong Formation in the late Carboniferous of the Eastern SichuanBasin is formed in the limited bay. And the original sediments is with low δ13C, δ18Onumbers and high87Sr/86Sr ratios in the mud–micrite, mud–dolomicrite, may beinfluenced greatly by fresh water, for its environment in rich supply of that. All kindsof karst rocks in the paleokarst reservoirs of the Huanglong Formation in the researcharea are affected by atmospheric freshwater, δ13C, δ18O numbers and87Sr/86Sr ratios inthe original formation approach that of atmospheric freshwater, which reflect itsancient hydrological conditions, fluid properties, isotopic source and its fractionationeffect. The intensely corroded and altered secondary limestones are affected by avariety of diagenetic fluids, in many times, so that δ13C, δ18O numbers reflect that phenomenon, while87Sr/86Sr ratios show the strong degree of the corrosion. We gotthe result that the diagenetic fluids are mainly atmospheric freshwater, aftercomparing the87Sr/86Sr ratios of each karst rocks. And with strengthen of thecorrosion, the low87Sr/86Sr ratio fluids in the layer will participate in the karstprocess.(3)Occurrences of natural fractures are mainly low angle and high angle obliquefractures, secondary is vertical fractures, horizontal fractures is rare to see;Development density of fractures is highest in second member of Huanglongformation, secondary is in third member, while worst in first member; There are twotypes of extensional fracture and tensile fractures in core description; Effect fracturestake part in73%with packing (material) are calcite and peat, and natural fractureshave good effectiveness. This research directs mainly at Indosinian to early Yanshanepoch and late Yanshan epoch to early Himalaya orogeny period when fractures areforming, which is on the basis of development, genesis and phase of fractures in studyarea, Composite maps of fracture distribution in study area are worked out forsynthesized stacking by prediction of distribution of two types fractures with ways ofsymbiosis cracks in fault control function and main structure curvature. This paperbelieve forecast the outcome of fractures distribution dovetails nicely with existingdata and manages to geomechanical background by evaluation of fracture statistics ofcores and logging interpretation result for fractures. |
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