Systematic Application of Pressure and Temperature Transient Analysis in an Oil Field: A Case Study

Pressure Transient Analysis (PTA) methodology has long enabled well testing to become a standard routine. Modern, well and reservoir monitoring and management practices are now unthinkable without the well test-derived estimates of KH products, skin factors, radii of reservoir boundaries, etc. Temperature data, measured together with the pressure, is widely available. Multiple methods for Temperature Transient Analysis (TTA) have also been developed, but have not yet gained due recognition. Few examples of a systematic application of PTA and TTA (or, in general, Pressure and Temperature Transient Analysis PTTA) on a field scale have been published. Given that the TTA radius of investigation is much smaller than that for PTA, the TTA tends to explore the near-wellbore properties including the near-wellbore permeability profile, depth of damage, multi-layer parameters, fluid properties, etc. This complements the far-field estimates made by PTA, resulting in the PTTA providing a more holistic and complete picture of the state of the reservoir and fluids around the wellbore. This work demonstrates a case study of a systematic application of PTTA methods to wells in a green, oil field. The wells are equipped with a state-of-the-art, downhole, permanent monitoring equipment. A user-friendly, bespoke toolbox has been developed to carry out PTTA analysis in this field. Dozens of transient events that occurred in the first few years of the field production life have been analyzed using PTTA. There are multiple examples of this PTTA analysis demonstrating improved characterization of the reservoir, near-wellbore, fluid, and multi-layer properties. This work will be insightful to those looking to find out what additional, useful information (like reservoir and fluid properties) can be extracted from the traditional well-test, transient pressure and temperature measurements at no extra cost.

Accounting for Fluid-Property Variations in Temperature-Transient Analysis

Summary Significant fluid-property variation can be induced with pressure and temperature dynamics in the reservoir associated with oil production. The existing analytical solutions for temperature-transient analysis (TTA) generally assume constant fluid properties, which can be invalid especially for cases of high drawdown and strong temperature signals. In this study, we present a method to account for the fluid-property variations in TTA. The method introduces corrections on fluid-property values as input for analytical solutions, considering the quasilinear behavior of the temporal Joule-Thomson effect on a semilog plot. The corrections are performed on four identified fluid properties in an iterative manner, which can be easily implemented in available temperature-analysis procedures. To validate the developed approach, we model drawdown- and buildup-transient-temperature signals with the fluid-property correction method for nondamaged and damaged reservoirs under different production rates and reservoir-fluid compositions. The analytical modeling results are compared with numerical simulations. In addition, by finding the dominating fluid property, a simplified approach of property correction is presented. Through application to example problems, we show that using the fluid-property correction method presented here can improve the permeability estimations by 60% for the conditions considered in this paper. We present a modified method for damaged reservoirs, which results in an additional 25% improvement on the permeability estimations. With these improvements, the applicability of TTA using analytical solutions can be extended from cases with limited sandface-temperature signals of a few degrees Celsius to stronger signals of 20 to 30°C.