Study On The Technology For Log Interpretation Of The Clastic Reservoirs Within The Donghetang Formation In The Tahe Oilfield, Xinjiang

The Tahe oilfield is located in the north of the Tarimu Basin. It has been provedthrough exploration that good hydrocarbon showing occurs in the sandstone segmentof the Donghetang Formation, Devonian System in the southwestern part of the Taheregion. The clastic reservoirs in the region are middle to low in porosity andpermeability.An analysis on logging response of the Donghetang Formation and acomputation of resistivity of strata in typical wells under conditions of differentparameters are carried out on the basis of collecting and processing related data.Meanwhile, environmental correction and normalization are made for the dataobtained by using different kinds of logging instruments, and then processing for thelogging data from each single well. The following are the achievements that havebeen acquired in this study.The Donghetang Formation consists of alternating beds of sandstone andmudstone, on the top of which there is a thick sandstone bed including gravel andcoarse to fine sandstone and having no pure coarse sandstone or pure gravel. Thesandstone has negative SP anomaly and low GR and resistivity. Three resistivitycurves obtained at deep, middle, and shallow depth of investigation are notoverlapped with each other, and porosity indicated by AC, CNL, and DEN is low.Negative seperation between deep resistivity and medium resistivity is becausethe amount of resistivity of strata increased owing to high resistivity of mud or poorpetrophisical properties is much more than that decreased due to high water saturationor less oil content. Thus, occurrence of oil or water layer should be judged not only bydifference in resistivity or lower resistivity zone, but by difference in salinity betweenmud filter and formation water, by petrophisical properties, oil fluidity, and so on.It is inferred according to statistic results of data obtained through microscopicobservation and petrophisical properties measurement that the lithologies of theDonghetang Formation are dominated by silt to fine sandstone, middle to finesandstone, and fine sandstone. The porosity and permeability of the reservoirs in theDonghetang Formation are mostly middle and middle to low , secondly middle tohigh and middle, and rarely low and low, respectively.A set of log interpretation models is established, involving shale content, grainmedian, porosity, permeability, water saturation, irreducible water saturation.Meanwhile, plates for determination of oil or water layer in the area and each well arebuilt in order to identify various kinds of fluid. Then logging data from all relevantwells are processed, showing obvious increasing in accordance of log interpretation.