Porosity Estimation in Volcanic Gas Reservoir

Complex and variable mineralogy of volcanic reservoirs leads to significant variations in matrix properties.Determination of matrix properties required for porosity calculation has proven to be problematic in Volcanic reservoirs.At the same time the presence of gas in the reservoir,which has a detrimental influence on most measurements used in porosity computation,complicates the situation.One new approach integrating ECS,Density and CMR for porosity calculation was introduced.Since rock matrix parameter is a function of rock chemical compositions and atomic arrangements,the MINCAP is used for core analyses in the studied area,and a relation expression is given using ECS log data to directly calculate volcanics matrix density and matrix neutron.On the base of calculating the rock matrix parameters,the DMRP algorithm is used for gas-bearing correction of reservoir porosity log curves,from which we derived a qualitative gas-bearing formation evaluation method.This is the first example to calculate matrix log parameters of continious formation depths with log data in the volcanics porosity calculation.The core analysis data and log data of subsequent wells have proved the above method is reliable and feasible(in the acidic volcanics formation log).But there are not many cores for MINCAP analysis,and the main rock for the analysis is acidic volcanics.This method is also a reference for calculating other complex lithologic reservoirs porosities.A useful auxiliary output of this method is a gas indication,which has proven very reliable in identifying gas bearing intervals in the interpreted wells.