Relationship Between Water Cut Characteristics And Reservoir Configuration Of Ordovician Carbonate Reservoirs, Tahe Oilfield Fourth Area

Ordovician fractured-vuggy carbonate reservoir of Tahe Oilfield, fourth area isformed by karstification. It is characterized by old layers, ultra-deep, taking karstfractures and caves as reservoirs. Accumulation condition is complex, reservoir spaceshapes vary, the distribution and flow of fluids are very special. Withoutsuccessfulexperiences or development model both domestic and overseas, all these peculiaritiesmake efficient exploration and development of these reservoirs a big challenge, toengineers all around the world.With the background talked above, this research seeks to understand the flow offluids underground better by studying how water cut changes with differentconfigurations of reservoirs, hoping to help take production measures such asstabilizing oil and controlling water and the target of improving ultimate recovery.This research starts with karstification, the origin of this kind of reservoirs,analyzes the process of karst and its control on the formation and transformation ofreservoirs and physical properties, and summarizes characteristics and exploration&identification methods of reservoir spaces. Single well conceptual model is alsoestablished through seismic analysis to ascertain the distribution of reservoir spacearound the borehole. Connectivity is analyzed with dynamic and static methods, theconfiguration and degree of connectivity of reservoirs are thus understood. Severalwater cut curves are compared and the Daily water cut–Total liquid production curveis taken to analyze the changes of water cut. The types of curves are divided intoascending, descending, sharp rise, sharp fall, terrace, fluctuating and flooding.For fluids in spaces of large scale, such as caves and large fractures, their flowpattern is pipe flow. What happens in spaces of small scale, such as micro-fracturesand dissolved pores, is seepage. The complexity of flow and heterogeneity ofreservoirs are what the main reasons for complex water cut changes really are. Ascending water cut often occurs in the presence of reservoir seepage whilesharp rise of water cut represents water has broken through into the bottom of well inthe process of piston flooding. Terrace type is a typical cave water productioncharacteristic. Descending appears mostly when drilled into a reservoir with constantvolume and limited water, or the well is drilled into several sets of different reservoirs.Fluctuating water cut represents a complex configuration of reservoirs.