The Character And Distribution Regular Analysis Of Tight Reservoir In Shihezi Formation In Shiguhao Region

According to sedimentary geology characters in study area and through manyanalysis of processors and many subjects knowledge such as sedimentology, geologyand well logging, this paper takes reservoir sandstone in Shihezi Formation ofShiguhao region in Ordos basin as searching objects, which has discussed characters ofsedimentary system, sedimentary facies distribution, lithofacies paleogeographic,reservoir sandstone and genetic types of reservoir sandbody, control factors of reservoir,character and distribution regular of high-quality reservoir from macro and microresearch with using logging and test analysis data. The cognitions and profits are asfollows:（1）Based on the analysis of regional tectonic evolution character in Shiguhaoregion and Ordos basin, this paper has discussed tectonic unit that Shiguhao regionbelong to, and searched systematically about development character of Burjans Nurfractures and its control action to basement, tectonic pattern, stratigraphic distributionand sediment in Upper Paleozoic（2）Based onthestratigraphicclassificationschemein productivepractice madeby North China Filiale of China Petrochemical Industry, the analysis of stratigraphicclassification carried out in Shihezi formation of Shiguhao region with using drillingand logging data and identifing lithology, electric property and sedimentary marks inand around study area. On the basis, lower Shihezi formation is made thin layer divisionthat the first member is divided into four thin layers（H1-1、H1-2、H1-3、H1-4）,secondmember is divided into two thin layers（H2-1、H2-2）,and the third member is alsodivided into two thin layers（H3-1、H3-2）.（3）According to sedimentary scheme and sedimentation character, continentaldeposit group is identified in lower Shihezi formation of Shiguhao region,which aremainly braided river sedimentary system with composite analysis of core observationand logging data, and the system comprise of channel and flood plain deposit subfacies,which develop microfacies as gravel lag-deposit of riverbed, channel bar andfloodplain. Distribution and evolution of sedimentary facies in Shiguhao region arecontrolled by tectonization and paleogeomorphic, and study area has been went through from Taiyuan stage of Late Carboniferous epoch to lower Shihezi stage of late EarlyPermian. This paper emphasis on sedimentary evolution of lower Shihezi formation inShiguhao region, through make certain sedimentary scheme in lower Shihezi formationto reveal lithofacies paleogeographic character and evolution regular in every thinlayer(the first, second and third member of Shihezi formation). On the basis, ourpurpose is to clarify distribution regular of sedimentary facies belt in every member oflower Shihezi formation of study area, the working thought is determining sedimentarymicrofacies types in single well,then making use of logging data from single wellfacies to plain facies with comprehensive analysis in all area.（4）This paper has searched systematically petrology, physical properties andpore structure character of reservoirs in lower Shihezi formation of Shiguhao region.The studies have shown that coarse to middle grain feldspathic litharenite are mainlithology. The whole reservoirs are tight with low-porosity and low-permeability, thethird and first member have good physical properties, while second member is bad.According to relationship between porosity and permeability, reservoir types of studyarea are mainly pore reservoir with local fracture-pore pattern reservoir. Pore types inreservoirs of lower Shihezi formation in study area can be divided into four types asresidual primary intergranular pores, secondary intergranular pores, inner dissolutionpores and fractures, and the above two have reservoir property with small-mediatepores and thin throat characters.（5）This paper interprets logging data of drilling wells in Shiguhao region andanalyses four natures character of reservoirs, which comprise of building math modelrefer to logging data to interpret pores, making certain of lower limit value of reservoireffective thickness, carrying out overall evaluation of reservoir in single well, workingout distribution map of effective thickness and pore of reservoirs in every section oflower Shihezi formation in Shiguhao region, and researching vertical evolution andplain distribution of reservoirs systematically. On above basis, there are three types ofreservoirs that are perfect, good and non-reservoir with overall evaluation, whichdivided from reservoir sandstone of lower Shihezi in Shiguhao region according tolithology, physical property and pore structures characters.（6）The development of reservoirs in study area are controlled by rock grainsize,rock composition, types and diagenesis of reservoir sandstone from comprehensiveanalysis of sediment, reservoir and production performance data. The studies haveshown that physical properties of reservoirs is proportional to rock grain and thecontent of quartz and feldspar, reservoir quality of quartzy sandstone, lithic quartz sandstone and lithic sandstone are from good to bad. In the process of diagenesis,dissolution and alteration help to improve reservoir quality, while consolidation,cementation and replacement make sandstone tight and porosity-permeability bad.（7）Basic geology characters of high quality reservoirs are analysed fromlithology, litho-facies, sedimentary microfacies and electronic property part, of whichare mainly developed in microfacies as distributary channels and channel bar with highenergy, and smooth box models character appear in logging curve. Box model in GRcurve, negative anomaly in SP, relative high value in AC and RT, while relative lowvalue in CNL and DEN to response gritstone or pebbly gritstone. High qualityreservoirs are divided and evaluated, and plane distribution of high quality reservoirsalso searched with analysis of chart intersection. Based on intersection way of AC-RTand AC-CNL, the first and third member are in accordance with developmentconditions of high quality reservoirs,so evaluation criterion of high quality reservoirs inthe first and third members is built respectively, and classified high quality reservoirsinto four types(Ⅰ-1、Ⅰ-2、Ⅱ、Ⅲ).At last, the plain distribution regular of high qualityreservoirs are determined.（8）On the above basis of sediment and reservoir analysis, forecast of favorableexploration areas in the first, second and third member has been respectively carried outwith practical exploration.