Research On Gas Welltesting Analysis With Wellbore Thermal Effect

The volcanic gas reservoir of Daqing has the characteristic of deep burial and high temperature. The gas well testing in the reservoir is difficult, and most of the wells are operated by surface open and shut-in method. During the process of pressure buildup, the larger temperature change existed in the wellbore affects the downhole pressure buildup dynamics, and causes the abnormity of pressure buildup curve in well testing evaluation. The homogeneous infinite reservoir will present composite or double porosity characteristics, and the true features of the reservoir are disguised. As the present well testing model does not consider the wellbore temperature change, the rationality and accuracy of the well testing results are affected. To solve the above problems, based on the thermodynamics knowledge, the temperature change law inside the wellbore under different production status, and the effect law of temperature on gas property parameter are analyzed and studied. Applying the related theory of thermodynamics, the temperature change model in the gas wellbore is established. Based on the seepage flow theory of gas well, the mathematical logic model for gas well testing is established considering the thermal effect. And in accordance with the mathematical logic model, the well testing theory plate under the thermal effect is established. The thermal effect law on gas well is analyzed on the basis of the theory plate to distinguish the effects of temperature inside the gas well on pressure curves, The transient well testing evaluation software of gas well is developed considering the thermal effect. The gas well data with abnormal well testing curves are interpreted by the software with the consideration the thermal effect, the parameters, such as, the formation permeability, skin factor, and the maximum temperature differential effect in the wellbore, etc, are given.The method is inspected and verified with the data from 14 wells and 18 layers. The error of simulated productivity is less than 20% compared with the real productivity. To compare with the real well productivity and test the simulated results, in 6 producing wells, the simulated results are applied to predict the medium and long term productivity. The simulated results of 5 wells are consistent with the real production, which demonstrates the parameters given by the well testing method considering the thermal effect reflect more accurately the real reservoir properties. The better results of the method shown in the real gas well testing analysis attains the goal of evaluating accurately gas well testing data with thermal effect, understanding and evaluating the reservoir correctly, and guiding the exploration and production of the deep gas well.