The Study Of Classifications And Characteristic Of Ordovician Carbonate Reservoir In Block 2of Tahe Oilfield

Ordovician carbonate reservoirs in block 2 of Tahe Oilfield are formed by two episodes of Supergene karst, and. have strong heterogeneity.Moreover, block 2 locates at the base of karst slope, and has weaker karstification than the top of the karst slope and different types of reservoirs and spreading. As the different formations between north and south of block 2, there are diversities in construction, faults, reservoirs.Through the analysis of its geological, well-logging and seismic data, we understand the feature and texture inside of this karst crack-cavity type reservoirs, which directly benefit the exploration and development of Tahe Oilfield and improving the recovery efficiency.There’re three types of Ordovician reservoir space in block 2 of Tahe Oilfield which include karst cavities, pore and fractures. Reservoirs are formed by the combination of reservoir space and classified into karst cavities type, dissolution pore connecting by fissures type, fracture type, and fissures – matrix type. Karst cavities type which is mainly composed of caves formed by karst is the most important type of block 2 of Tahe Oilfield and distributes in the distance range of 0-100 m to the unconformity and is mostly in O2 yj and O1-2y in the northern of block 2. Dissolution pore connecting by fissures type which covers dissolution pore and fissures is the main type. Fracture type is made of tectonic fissures, which are the most, and diagenetic fractures and other kinds of fissures. Fissures – matrix type is made of stylolite and diagenetic pores.These four types of reservoirs can all be found in the study area: karst cavities type which is characterized by the large number but small scale mainly develops in the northern. And dissolution pore connecting by fissures type and fracture type mainly develop in the southern. There are also four kinds of horizontal distribution patterns i: hypergene karst river patter, karst tunnel pattern, paleotopography pattern and fissures pattern. Vertically, there are three episodes of karstification, and they are 0-40 m, 60-100 m and 150-200 m away from the unconformity respectively. Qualities of reservoirs are determined by lithology, structures and cracks, paleotopography and ancestral rivers, unconformity, diagenesis and ect. Based on study of reservoirs, block 2 is divided into 22 fracture- cave units.