Experimental Study On Flow Mechanism Of Fracture-cavity Type Carbonate Reservoirs

Carbonate oil and gas reservoirs are widely distributed around the world,and their reserves of oil and gas account for more than half of total oil reserves of the world.However,fracture-cavity type carbonate reservoirs are characterized by complex structures,diverse types of reservoir spaces,deep burial depth,strong heterogeneity of reservoirs,poor connectivity,complex oil-water relationships,and large differences in natural energy among various types of reservoirs.So,the fluid flow in the fracture-cavity medium is more complicated than the traditional sandstone medium.This paper focuses on the basic geologic characteristics of the target block,and studies the geological characteristics of the target reservoir and fluids for the problems of rapid production decline in volatile oil reservoirs,difficulty in stable production,and low recovery of volatile oil in the south of the Halahatang of the Tarim Oilfield.To characterize and summarize the conceptual model of the typical fracture-cavity type carbonate reservoir.Then,based on the design of the fracture-cavity type carbonate rock physical model,some simulation experimental study of pressure-keeping development were carried out.Some results and conclusions have been obtained through this study:(1)The rock in the main reservoir section of the target block shows oil-wet in wettability,and consists of calcite.(2)The reservoirs in the target block can be divided into three types:single cave-fissure type,multiple cave-fissure type reservoirs,and fracture-hole type.Multi-cavity-fractured reservoirs accounted for the most.(3)Physical modeling experiments of pressure-maintaining development show that,for single-cavern-fractured and multi-cavity-fractured reservoirs,pressure-keeping development by injecting water or nitrogen can increase the recovery of volatile oil.For crack-hole reservoirs,either use of water or nitrogen for pressure-keeping development,the effect is unsatisfactory.(4)The main mechanism for pressure-keeping development of volatile oil reservoirs is to supplement formation energy and re-dissolve the dissolved gas.Therefore,the injection time for pressure-keeping development should be selected before the volatile oil has undergone substantial degassing.(5)Based on the experimental results and mineral experience,the scope of the technical indicators such as well selection principle,pressure-keeping media type,timing for injection,amount for injection,and time for well shutin during pressure development is given.The simulation results of the same model experiment are verified by the example well in the mine.