On a Well Test Analysis Method Accounting for pre-Test Operations

We propose to use regular monitoring data from a production or injection well for estimating the formation hydraulic properties in the vicinity of the wellbore without interrupting the operations. In our approach, we select a portion of the pumping data over a certain time interval and then derive our conclusions from analysis of these data. A distinctive feature of the proposed approach differing it form conventional methods is in the introduction of an additional parameter, an effective pre-test pumping rate. The additional parameter is derived based on a rigorous asymptotic analysis of the flow model. Thus, we account for the non-uniform pressure distribution at the beginning of testing time interval caused by pre-test operations at the well. By synthetic and field examples, we demonstrate that deviation of the matching curve from the data that is usually attributed to skin and wellbore storage effects, can also be interpreted through this new parameter. Moreover, with our method, the data curve is matched equally well and the results of the analysis remain stable when the analyzed data interval is perturbed, whereas traditional methods are sensitive to the choice of the data interval. A special efficient minimization procedure has been developed for searching the best fitting parameters. We enhanced our analysis above with a procedure of estimating ambient reservoir pressure and dimensionless wellbore radius. The methods reported here have been implemented in code ODA (Operations Data Analysis). A beta version of the code is available for free testing and evaluation to interested parties.