Luis Ayestaran

Interpretation of a Pulse Test in a Layered Reservoir

An interwell pressure test, designed and implemented as a pulse test, was performed in the Arab zones of an offshore oil field in Abu Dhabi. The interpretation of three pulses yielded inconsistent results for transmissibility and storativity. The pressure response data were interpreted with a twolayer analytical model after a numerical simulator was used to modify the pressure response for the interference from a third well. The two-layer analytical model provided an excellent match of the modified pressure response. This paper concludes that conventional pulse-test interpretation methods cannot be satisfactorily applied to the pressure response in a two-layer system.

Well testing and analysis techniques for layered reservoirs

This paper presents new testing and analysis techniques to obtain individual-layer permeabilities and skin factors for layered reservoirs. The new multilayer testing techniques consists of a number of sequential flow tests with a production logging tool that simultaneously measures the wellbore pressure and flow rate at the top of each layer. Two different analysis techniques are presented to estimate layer parameters. The first technique, which is the logarithmic convolution method, estimates the approximate values of parameters. The second technique, which is the nonlinear least-squares estimation method, improves the first estimates. It is shown that layer permeabilities and skin factors can be estimated uniquely from simultaneously measured wellbore pressure and flow-rate data that are acquired from all layers sequentially. It is also shown that these individual-layer parameters cannot be estimated from the conventional drawdown- or buildup-test wellbore pressure data. Several synthetic examples are presented to illustrate the application of multilayer testing and analysis techniques.

Deconvolution of wellbore pressure and flow rate

Determination of the influence function of a well/reservoir system from the deconvolution of wellbore flow rate and pressure is presented. Deconvolution is fundamental and is particularly applicable to system identification. A variety of different deconvolution algorithms are presented. The simplest algorithm is a direct method that works well for data without measurement noise but that fails in the presence of even small amounts of noise. The authors show, however, that a modified algorithm that imposes constraints on the solution set works well, even with significant measurement errors.

Estimation of the Permeabilities and Skin Factors in Layered Reservoirs With Downhole Rate and Pressure Data

This paper addresses the problem of estimating horizontal and vertical permeabilities, skin factor, and average fluid pressure within the drainage area in each layer in a multilayered reservoir in the presence of formation crossflow between the layers and commingling through the wellbore. A multistep testing procedure is proposed that involves downhole measurement of the pressure and fluid flow rate. The measurements are made successively above the individual layers as transients are induced in the reservoir. A history-matching procedure is used to analyze the data from the entire multistep test simultaneously. The performance of this approach is compared with that of separate, conventional interpretation of each step in five examples with synthetic data. The simultaneous analysis benefits from the synergy between the steps and consistently yields better estimates. A linearized sensitivity analysis is developed to determine the probable errors in the parameter estimates. It indicates whether a given set of measurements with a given level of measurement noise contains sufficient information to determine the individual parameters uniquely.