Logging Characterization Of Ordovician Carbonate Reservoirs In Second And Tenth Block Of Tahe Oilfield

The Ordovician carbonate reservoirs in Tahe oilfield are characterized by deep burial,and they experienced multistage of tectonic activities and karst transformations.Compared with the fractured carbonate reservoirs,conventional clastic reservoirs,the Ordovician carbonate reservoirs in Tahe oilfield are characterized with various reservoir types,high heterogeneity and anisotropy.There are many karst fracture-cave reservoirs coexisted with the micro-pore type reservoirs.There are many problems existing in the logging evaluation methods for the complex Ordovician carbonate reservoirs in second and tenth block of Tahe oilfield,such as difficulty in quantitatively calculating reservoir parameters.This paper aims at these problems,and analyzes the lithology and electrical properties of various reservoir types from the aspects of lithological characteristics and reservoir formation mechanisms on the base of the lithology recognition and division of reservoir type.Then the numerical stimulations of log curves together with the recognition methods of various types of reservoirs are studied in detail by using cores,logs,seismic files and production performances,calibrating with cores,conventional logs and image logs.Therefore the reservoir parameter can be characterized in this way,and then a suit of methods applicable for the logging evaluation of carbonate reservoirs in Tahe oilfield are proposed.It can provide the reservoir parameters for geological modeling and provide for oilfield development.Based on the above works,the below conclusions could be drawn:(1)Four types of carbonate reservoirs are developed in the Ordovician of Tahe oilfield,and they are cavern type,fracture type,fracture cavern type and micro-pore type.The reservoir types are dominated by fracture type and fracture cavern type,whereas the micro-pore type is relatively rare,in contrast the fracture type is generally absent.The micro-pore type reservoirs belong to typical tight reservoirs,and they are almost developed in the grainstone and batocera limestone,which have a large potential for the late-stage development.(2)The lithology of the Ordovician carbonates in Tahe oilfield is dominated by micrite,grainstone,leopard limestone,karst breccias and transition lithology such as marlstone,lime mudstone.Considering that the lithology has an important control on the development of micro-pore type reservoirs,and on the basis of the rock-electricity analysis,the logging parameters which are sensitive to the lithology are chosen,and the Crossplot and Bayesian Discriminant Analysis were adopted to effectively recognize the lithology in the Tahe oilfield,and the accuracy is more than 86.0%.The distribution law of micro-pore type reservoirs is revealed under the control of sedimentology and diagenetic modifications.(3)There are many problems existing in the complexity of logging information of various reservoirs types such as cavern type,fracture cavern type and micro-pore type,for example,the complexity of logging information is high and it's difficult to recognize the reservoir.This paper aims at these problems,and proposes the modeling of the dual lateral logs of cavern type,fracture cavern type reservoirs,and determines the reservoir parameter affecting the logging response characteristics of dual lateral logs from the aspects of forward modeling,and this provides a new method for the reservoir type recognition using conventional logs.(4)The energy entropy of each type of logging parameters is studied using empirical mode decomposition(EMD)method,and the types of carbonate reservoirs were able to be accurately identified by using Fisher discriminant.Therefore the methods using EMD methods are proposed to recognize the reservoir types.This method reduces the uncertainty in choosing the logging values of typical single layer,and realizes the recognition of various types of reservoirs using well logs,and the accuracy is as high as 96.4%.(5)The reservoir parameters are quantitatively calculated by optimizating the conventional well logs,array acoustic logging and image logs.A new brittleness index calculation model is established based on constrains of various mineral constituents,and then the continuous logging characterization of complex carbonate reservoirs in a single well could be realized using conventional well logs.The above results proposed in this paper could not only establish the logging evaluation methods for complex carbonate reservoirs with various reservoir space such as pores,fractures and caves,but also would provide guidances for the further petroleum exploration and development of the carbonate reservoirs in Tahe oilfield.