Data Acquisition In Pumping Wells

Abstract

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. Introduction Pressure buildup analysis in pumping wells has suffered from the difficulty in directly measuring pressures at the bottom of the well. Often, the only reasonable method of acquiring pressure data in such wells is to combine casing pressure and Fluid Level Measurements (FLM) with estimated fluid densities to indirectly estimate the bottomhole pressure, which is then analyzed. In such situations, the only practical means of gathering pressure data is the use of the FLM method to determine the fluid level in the casing. The Fluid Level Measurement can be used for indirectly computing bottomhole pressure and rate of afterflow in pumping wells. This calculation uses fluid level and casing head pressure data obtained during a transient test. During pressure build-up tests, free gas returns back into solution as the pressure increases in the wellbore. This causes a reduction in both oil density and free gas flow rate. A mass transfer(1) between the oil and gas phases occurs in the well annulus during either flowing or build-up conditions. In the paper presented, Hasan & Kabir(7) method was used to calculate bottomhole pressure. The bottomhole pressures used in the analyses contain errors due to measurement of the fluid levels and due to uncertainties in the fluid densities. These measurements can easily lead to errors of several percent in the downhole pressure calculations. The fluid level measurement is a direct indication of fluid accumulation in the wellbore (wellbore storage) and gas segregation during a build-up testing when the amount of gas in the fluid column changes. Description of Fluid Level Measurement Methods The Fluid Level Measurement became very important as a well testing technique for pumping wells. Many hydrodynamic models and empirical correlations have been developed to indirectly calculate the bottomhole pressure and the afterflow rate during pressure buildup tests in pumping wells. The use of the Fluid Level Measurement technique to determine bottomhole pressure and bottomhole rate requires an estimate of the gas void fraction in the liquid column of a pumping well annulus. Few correlations relating the "annular superficial gas velocity" are available for saturated oil columns, the most used among them are Godbey and Dimon(4), Podio et al.,(5) and Gilbert as reported by Gipson and Swaim(6). The validity of using FLM methods in well testing has been assured because many actual examples have shown good consistency after the downhole pressure was measured as shown in Figure 1. The downhole pressure was calculated by computer program using methodology described below.