Fluid Flow Characteristics And Development Policy Research Of Fracture-vuggy Carbonate GAS Reservoir With Bottom Water

Fracture-vuggy carbonate reservoirs have complex and multi-scale pore structure as well as strongly randomly distributed and heterogeneous fractures and vugs.What's more.different carbonate reservoirs have different development degree of fracture-vuggy pore structures,and the reservoirs have complex oil-gas-water relationship.The foregoing reservoir conditions make it difficult to develop this kind of reservoirs.ZDX fracture-vuggy carbonate gas reservoir with bottom water studied in this research has reservoir characteristics like low porosity,low permeability,multiple payzones and strong heterogeneity in both vertical and horizontal directions.Bottom water cones and gas-water coflow occurs in the reservoir during development.Researches on gas-water relative permeability experiment,bottom water invasion mechanism,storage-flow modes and technical development policy were conducted on this fracture-vuggy carbonate gas reservoir,which has important significance on efficient development of this kind of gas reservoir.In-depth and comprehensive researches,like experiments,well testing and numerical simulation,were carried on to study the difficulties in the development of fracture-vuggy carbonate gas reservoirs.Full diameter matrix cores extracted from actual carbonate fracture-vuggy gas reservoir were used to obtain desired fracture-pore cores and fracture-vug cores with artificial fractures and/or vugs.Unsteady gas-water relative permeability tests were conducted on the foregoing cores,under conventional pressure and temperature,as well as under high pressure and high temperature with a newly established gas-water relative permeability method for high pressure and temperature conditions.Then bottom water invasion mechanism experiment of fracture-vuggy gas reservoir was conducted on the full diameter fracture-vuggy cores with the full diameter core coreflood device.In addition,reservoir numerical simulation software Eclipse was used to study the invasion rule of bottom water in fracture-vuggy gas reservoir.Storage-flow modes of fracture-vuggy carbonate were classified into several categories and modern well testing interpretation software NWTIS(V2.0)was applied to interpret the real data of this gas reservoir.Finally,development policy of the ZDX D2 gas reservoir was established.Main achievements of this research:(1)Cores with desired fracture-vug system have been obtained by manufacturing artificial fractures and/or vugs on full diameter matrix cores that were extracted from actual carbonate fracture-vuggy gas reservoir.This provides necessary and basic models for flow experiment of fracture-vuggy carbonate reservoirs.(2)This study has established the first high temperature and high pressure gas-water relative permeability test method that considers dissolution of gas and water in each other during gas-water flow under high temperature and high pressure.Residual water saturation in horizontally connected fracture-vug core under high temperature and high pressure is 11.77%lower than that under conventional temperature and pressure,and relative gas permeability at residual water saturation doubles.For vertically connected situation,residual water saturation under high temperature and high pressure is 15.17%lower than that under conventional temperature and pressure,and relative gas permeability triples.Therefore,the high temperature and high pressure has significant influence on relative permeability in fracture-vuggy gas reservoir.(3)Bottom water has significant effect on the gas production per pressure drop in the medium phase of gas reservoir development,and water production switches from "step"rising character to the water channeling in the fracture.Depletion rate mainly affects gas production in the medium and later phase,and water production rate and cumulative water production can be increased.And the water production switches from "step" rising character to the water production from fracture.For gas reservoir with aquifers 5-20 times larger than itself,the gas recovery difference can be up to 18%.(4)If the bottom aquifer connected with the fracture-vuggy gas reservoir has volume less than 40 times as large as the reservoir,invasion capacity of the aquifer strengthens,drive mode transforms from gas drive to water drive,the stable production period shortens,and water production and water-gas ratio increases as the increase of aquifer energy.While for gas reservoir with aquifer that has volume more than 40 times as large as the reservoir,influence of aquifer on gas reservoir performance reaches a plateau value.For invasion velocity in ascending order,gas and water production law is similar to that with increasing aquifer volume.(5)Interpretation results of the well testing in ZDX carbonate fracture-vuggy gas reservoir show:more dual-porosity and single-permeability fracture-vugs,strong heterogeneity in the reservoir,effective acidizing(acid fracturing),some wells present artificial fractures,and areas with natural fractures are located around the western fault of GST gas reservoir.(6)The D2 section in ZDX is a depletion drive gas reservoir,so it can be developed by depletion.D4 and D2 are developed separately for different fluid properties and pressure system.The D2 gas reservoir is mainly developed by vertical wells,and deviated wells or horizontal wells are also considered in areas without fractures.The reasonable well spacing is 1.0?2.0m,and the reasonable gas production rate is 1%?2%.A systematic research method combining fluid flow characteristics,bottom water invasion,well testing and development policy has been established for fracture-vuggy carbonate gas reservoir with bottom aquifer in this research.This provides theoretical and practical significance for development of these complex reservoirs.