The Study On Reservoir Characteristics Of Chang6in C33Area Of Chuankou Oilfield

Chuankou oilfield belongs to one of23oilfield affiliated with Yanchang Oil FieldCO.,LTD. And C33area is as the main exploitation of southern Chuankou oilfield, in whichuppermost oil layer is Chang-6reservoir of Yanchang Formation. Oil-bearing area can reach to12.2km2and reported proven reserves have numbers of559.4573tons. However, with the theever growing needs of energy by domestic industries, petroleum industry is faced with aserious situation.For solving these issues, improving the oilfield productivity and adapting to thedevelopment demands of efficiency development of water injection, Based on analysis of theprevious achievement and basic data and combining with geology, logging, production testdata and productive dynamic characteristics, this study aims to solving the problems in C33area of Chuankou oilfeild, including strong horizontal heterogeneity in planes, inter layers andinterior layers, water driving wave and limited volume during waterflooding and low degree ofproducing reserves. And this article has a detailed research on depositional and reservoircharacteristics, especially on petrology, diagenesis, physical property, pore structure,anisotropy and percolation. Then this research could establish the reservoir classificationstandard and further reservoir evaluation for comprehensive adjustment, measures ofexcavating remaining oil potential and efficient and rational development of reservoirs. Theresearching contents conclude the following three parts:1)reservoir petrology and diagenesis.2)pore structure and physical property.3)detailed characterization on anisotropy.Finally, this study gets the following conclusions:1)The lithology of Chang6reservoir ismainly gray fine-grained feldspar sandstone with lower mineral maturity, high structuralmaturity, which could indicate a low-energy and stable sedimentary environment.2)Chang6reservoir has strong diagenesis which is between late A phase and early late B phase. The mainreasons of destroying reservoir porosity and decreasing permeability are compaction andcementation of carbonate, clay minerals and laumonite. But the development of clay filmformation and dissolution protect primary pores and the secondary pores and improve the reservoir physical properties.3)The max porosity of Chang6reservoir is18.06%. Minimumporosity is1.28%. Average porosity is9.21%. The max permeability of Chang6reservoir is14.10×10-3μm2. Minimum permeability is less than0.16×10-3μm2. Average permeability is1.44×10-3μm2. Chang6reservoir could be defined as low pore and low permeability reservoir.4)The pore types of Chang6are residual intergranular pore, chemical erosion intergranularpores, chemical erosion intragranular pore, pore in the filler content, pore in the filler contentin chemical erosion, moldic pore, authigenic mineral intercrystal pore and fracture pore. Thepore assembly types are mainly Residual intergranular pore type, intergranularpores-micropore type, corrosion holes-micropore type, micropore type and compound type,which belongs to orifice-thin throats type and orifice-micro-thin throats type. According to rate-controlled test, distribution interval of Chang6throat radius is between0.2μm and0.7μm.The distribution interval of Chang6pore radius is between100μm and200μm. Throatdistribution curve is fine. The pore is coarse. It is nearly normal unimodality. According topore-throat classification standards of clastic rock, reservoir pore of Chang6is bigger poresand thin throats. The connectivity and tortuosity of the throat have a significant influence onpermeability.5)Statistic analysis of data shows Chang6reservoir in researching area appearsmedium to strong heterogeneity. But due to existence of micro-fracture, the heterogeneity ofChang6reservoir is more serious. And with constant progradation of sand in delta front, theheterogeneity of reservoir shows stronger trend.6)Chang6reservoir belongs to the extremelylow permeability reservoir which shows different seepage characteristics with normal reservoir.7)Based on the comprehensive analysis on reservoir physical property, microscopic reservoirpore structure characteristics, capillary pressure curves characteristics and reservoirheterogeneity characteristics, meanwhile combining with lithology and oil-bearing strata,Chang6reservoir in researching area could be divided into four types which are good(I type),medium(II type), bad(III type) and non(IV type) reservoir. And Chang611is mainly I+II typereservoir. I+II type reservoir of Chang612is accounting for57%. I+II type reservoir of Chang613is accounting for37%.