Abstract
Calculating of bottomhole flowing and shut-in pressures and bottomhole flowing rates, based on fluid level measurements and casing head pressures was combined with a convolution method of the build-up interpretation, for vertical and horizontal wells. The downhole pressures and rates were calculated using a mechanistic model(7), which shows good accuracy after comparing with downhole gauges measured data. The main uncertainty still remains the accuracy of fluid level measurement and water content in the annulus fluid, especially during well clean up period, which influences the density of the casing fluid column.
During the shut-in period, conventional pressure build-up analysis (Horner and derivative) and convolution methods were compared with the purpose of showing the advantages of the convolution method over the conventional. Consequently, the well test can be more rigorously interpreted by using convolution rate analysis, and the shut-in time is reduced by three folds, leading to economic advantage of testing costs saving.
The real time knowledge of bottomhole pressure and rates can be used to adjust the optimum downhole pump working regime, avoiding two phase flow through downhole pump and to perform conventional and convolution methods of interpretation without deploying bottomhole gauges. Majority of "brown fields" are equipped with different kind of artificial lift system including positive and dynamic displacement pumps. A fluid level measurement combined with a convolution method leads to an improvement of the production and operating economics of different types of artificial lift systems (SR, ESP, PCP, etc.) and can be used, as well, as a reservoir management tool. This paper includes actual field examples, with solutions that can be applied in the completion and testing of pumping wells. A field experience and subsequent achievement with downhole pumps testing in low permeability oil reservoirs are presented in this paper.
