低孔隙白云岩气藏的测井优化处理解释

LOG OPTIMIZATION PROCESSING INTERPRETATION OF DOLOMITE GAS RESERVOIRS WITH LOW POROSITY

低孔隙白云岩气藏以孔隙度低、渗透率低、含水饱和度高和岩石矿物成分复杂为特征，这些因素导致测井响应的模糊性以及问题的多解性。文章提出一种新的测井解释模型，其特点是：地层分为固体与流体两大部分，骨架与泥质分开，有效孔隙分为含气、含水孔隙度；只用孔隙度测井与自然伽马测井信息构成优化解释的响应方程组，电阻率测井不参加优化；地层按泥浆径向不同侵入深度分带进行优化计算。根据这一模型，选择可变误差多面体法作数学处理，它允许在一定的误差范围内，中间解可以不满足约束条件，并随着接近于问题的最优解，这个误差范围就越来越小，最后收敛到最优点。该算法适应范围广，即使函数的性质很差时，仍然可以得到比较可靠的结果，并且其结果对初值的依赖性弱，稳定性强。对陕甘宁盆地中部低孔隙白云岩气藏的十余口井测井资料进行了解释处理，其结果与实验数据和国外测井软件作了对比，取得了满意的效果。

The characteristics of low porosity, low permeability,high water saturation and complex minerals of dolomite gas reservoirs cause log resPOnses confused and log interptetutions with several possibilities. A new log interpretation model is formulatEd. its distinguishing features are that a reservoir is treated as two pertS of solid and liquid, separating framework from shallness. dividing effective porosity into two types of gas-bearing and water-bearing ; only porosity logs and .natural gamma ray log take part in the optimizing process, no resistivity log is included ;the reservoir is radially divided.into several zones by its mud-filtrate invasion profile and these zones are interpreted serrately. Suited to the model, an optimal algorithm with flexible tolerance is employed. It permits that,within the error margin and intermium solution may not correspond to the assumed conditions, but it as advances toward the optimum, this error margin is becoming more and more narrow till at last the solution convetges to the optimum one. The algorithm has a wide application. It can work even when the objective function is not a standard one and it depends little on an initial solution. Through processing the log data of over 10 wells from the dolomite gas reservoirs in the central part of Shanganning Basin and compering the resultS and experimental data with those processed with oversea software, satisfactory results are obtained.