Seismie Attribute Analysis And Sand Prediction In Bacan1Block In Bachu-maigaiti Area Of Tarim Basin

Bachu-Maigaiti region is located in the western of Tarim Basin,covering twosecondary structural unit:Bachu uplift in western of the central uplift andMaigaiti slope in Southwest Depression,structure of the district is complicated.The Silurian and Devonian system of Bachu-Maigaiti region is the majorresearch object of this paper.The strata of this region from bottom to toprespectively are:Kepingtage formation,Tataelta formation, yimugateu formation,Cozertag formation and Donghetang formation.Three-dimensional block of1well area is located in the junction of two secondary structural units and isconductive to the formation of lithologic reservoirs. But because of materialresources in the study area has a short duration and changes quickly, so theprediction of sand body in this area very difficult.The seismic attributes are an important basis of the sand bodies study, inthis paper extracts several properties to predict the sand body, eliminating thelimitation the use of a single property prediction，it combined with expertoptimization，selected eight kinds of seismic attributes, respectively: isochron,the total absolute amplitude, RMS amplitude, average energy, total energy, theaverage reflection intensity, the reflection intensity slope and meaninstantaneous frequency. Advantage of this method:①the selected propertieshave a clear physical meaning, in line with the geological law;②the selectedproperties are higher correlation with inoue sandstone thickness can reflect thesand body;③a lot of property types,using this methodcan can improve workefficiency. According to the response sensitivity of the sand thickness within thethickness of different strata， the authors weight to extract andoptimizeselected eight kinds of seismic attributes with eigenvalue coherencealgorithm.Based on the above process，the authors obtain non-dimensionalpseudo-sandstone thickness trends，which with the degree of the best withthe actual data.In the Kepingtage period sand-body enter from the northwest and widelydeveloped in the study area, Sand body of the first phase of the Kepingtageformation entered from the southwest into the study area, and depositedextensivly,retreated to the northwest; the second phase of this period,a thinsand body entered from the southwest into the the study area and develepedsporadically, sand body had a slow thiner trend.The Tataelta formation period sand body retreat to the northwest andbecome more thin.The sand body in the first phase of the Tataelta formationperiod continued to become thin, and distributed sporadically;the secondphase of this period,a thin sand body entered into the study area from thesouthwest,extended to the contemporaneous fault,and then retreated along tothe southeast;the third stage of this period,a thick sand body rapidly enteredfrom the northwest into the region, made a deposition of thick sand bodies inthe full region.According to Yimugateu formation the scope of sand bodies reduce toMinimize.In the first phase of Yimugateu formation,the sand body became thinand retreated to the south,only distributed sporadically in the south part;thesecond phase of this period,one thin sand along the fault extended from thesoutheast to the middle, the sand bodies distributed sporadically,moved to thenorthwest; the third phase of this period,the distribution of two strong sandbodies entered from the northwest and southeast into the region,this regioninto the full deposit stage.Cozertag formation sand body inheritants the basic distribution on theprevious period.The first phase of Cozertag formation,the sand body became thin,and retreated to the southeast, and distributed sporadically;the secondphase of this period,the sand body entered from the southwest into theregion,dispersed and moved to south, while a thick sand body entered fromthe northwest to this area;the third stage of this period, another strong sandbody entered from the southwest to this area, and convergenced with the sandbody from northwest, making the total deposit of thick sand body in thisregion,the emergence of shapes will remained basically unchanged,the overallthickness trended to thinner.During the Donghetang formation sand body entered the study area from thenorthwest again.The first phase of Donghetang formation,the sand bodyinherited the shape of last stage,and increased in the thickness;the secondphase of this period, sand dispersed moved to south in a minimum scope,show a strip distribution; the third stage of this period,sand body reboundedin the region, the deposition of sand body had features of thiner and widelydistributed.There are still many problems to be studied further by using seismicattributes to predict sand body, the accuracy of this method also have differentpoint of views,but as a way to improve the predictive ability of the sand bodyand in a line with the geological laws, should be fully affirmed its practical value,I believe this approach will further improve and develop in constant explorationand the application of practice,make its due contribution to petroleumexploration and development.