致密储层特征曲线分析常见问题及对策

致密储层低渗透率、压裂改造等特点,使得油气井呈现长时间的非稳态线性流,特征曲线方法被广泛应用于该类井渗透率、裂缝参数解释和产量预测,但实际井应用中常遇到时间均方根特征曲线"负截距"现象、变产—变压、油气两相、特征曲线多直线段等多种问题。通过大量的数据检验、理论分析和方法论证,对现场应用面临情况形成认识。研究认为:特征曲线"负截距"出现的原因,可能是原始地层压力偏小或生产时间零点值定义过早;运用物质平衡时间和线性叠加时间,可处理变产—变压问题,建议油井采用线性叠加时间、气井采用线性叠加拟时间或物质平衡时间;油气两相同产井可采用产量折算或两相拟函数法进行处理;多段线性流诊断须在双对数曲线上有明显的特征;在分析流程方面,推荐采用流动物质平衡方法计算储量和裂缝半长,从而计算渗透率。

COMMON PROBLEMS ANALYZED BY THE CHARACTERISTIC CURVE AND THEIR COUNTERMEASURES FOR THE TIGHT RESERVOIRS

The tight reservoirs are characterized by the low permeability,fracturing increment and so on,the longterm non-stable linear flow is caused for the oil and gas wells,so the specialized curve method is widely used in these wells to interpret the permeability,fracture parameters and so forth and moreover to predict the production.However,in the actual application of the well,the following so many problems are met:“negative intercept” phenomenon for the characteristic curve of the root mean square of the time,variable rate-variable pressure,oil and gas phases,multi-linear portions and so on.With the help of a large number of the data test,theoretical analysis and method demonstration,the faced conditions in the field application were understood.The study shows that the reasons of the “negative intercept” occurrence are maybe the rather lower initial formation pressure or the earlier defined start time of the production;the variable rate-variable pressure problem can be settled by the material balance time and linear superposition pseudo-time,especially for the gas wells,the second time is suggested for the oil well;the well with oil and gas production can be treated by the discounted production or two-phase pseudo-function;the obvious features are necessary in the log-log curve for the multi-linear portion diagnosis;in terms of the analysis procedure,the flowing material balance (FMB) method is recommended to calculate the reserves and fracture half-length,and then the permeability can be calculated as well.