Lessons learned from Wireline Formation Testing with Single and Multiple Probes

摘要

Previously there were few RFT data available for the Wararnformation of the Greater Burgan field. Therefore, duringrnrecent drilling, pressure measurements were made torninvestigate if vertical pressure equilibrium exists in thernformation after a production history of more than fifty years.rnThe erratic nature of measured pressure profiles indicates thatrnvertical communication is poor in the reservoir.rnIn each of the pressure measurements, a single probe wasrninserted into the mud filtrate zone, and then about 20 cc ofrnliquid was collected. In addition to obtaining the pressurernvalue, we also derived the permeability value by diagnosingrnthe pressure derivative signatures. Multiple probes were alsornused to evaluate vertical permeability over an interval of 2.3rnfeet. This paper describes how we analyze the data andrnovercome the problems encountered. We demonstrate thatrn3D-reservoir simulation of the formation test can improve thernquality of data interpretation. A summary of the analyticalrnmethod development is also given.rnDue to the high precision, 0.01 psi, of the quartz gauge, thernsingle-probe pressure derivative data quality was satisfactoryrnfor low permeability sands and the analytical method couldrnderive both the horizontal and vertical permeability valuesrnsuccessfully. However, for high permeability sands, therernoften existed a pressure hump immediately after shut-in and itrnresulted in unrecognizable signatures.rnA non-linear regression method was used to interpretrnmultiple-probe test data. However, sometimes a simultaneousrnpressure match for all the probes was difficult to achieve byrnthe analytical model. 3D finite-difference simulation wasrnrequired to fit the data and characterize the geologicalrnheterogeneity. Single-probe pre-test results were used tornprovide a good initial permeability guess for the numericalrnmodel. Gamma ray and formation image loggings were provenrnvaluable to determine the layering of the numerical model.rnFinally, core measurement and buildip test results wererncompared with formation test results.