A New Method to Identify and Quantify Hydraulic Communication Between Isolated Reservoir Systems Using Pressure-Transient Data

Abstract

A new analytical procedure is presented to identify hydraulic communication and quantify the corresponding fluid crossflow rates and connectivity between two originally non-communicating reservoir zones using pressure-transient data. The new method is applicable to a wide range of communication mechanisms, including inactive commingled-completion wells, conductive fractures and faults, in addition to behind-casing completion problems. The impact of interference is also captured by handling an unlimited number of wells and communicating media. The solution uses pressure-transient data effectively to diagnose communication and estimate the amount of transported fluids. The new formulation is a general formulation for handling an unlimited number of producing wells and communicating media, which helps analyze pressure responses under the influence of interference. The reservoir system under consideration is assumed to be two-dimensional with two initially-isolated reservoir zones, intersected by an arbitrary number of wells, part of which are active producers while others can be penetrating wells with commingled completion, in addition to other communicating media. The well test duration is assumed long enough for the pressure-transient data to be affected by fluid communication. To demonstrate the applicability of the new model, a synthetic case study is presented to diagnose a fluid-communication mechanism. The system under consideration consists of two isolated reservoirs and two wells: a single producer completed in the top reservoir in which pressure responses are measured, and an offset well connecting both reservoirs through a fluid communication mechanism. Using the model, type-curves have been utilized to diagnose the hydraulic communication in the offset well. The connectivity of the communication channel in the offset well is also estimated by matching the pressure-transient responses of the model with the measured data. The rate of crossflow between the two reservoirs is also quantified as a function of time. It is observed from the log-log plot that higher connectivity values of the cement sheath causes a steeper merging ramp in the transition region, following a period dominated by the producing reservoir. Although the rate of crossflow depends on the magnitude of the connectivity, it is observed that there is an upper limit controlled by the rock and fluid properties of the individual reservoirs. In addition, the pressure regime at the location of the offset well plays an important role in the rate of crossflow. This study presents a novel analytical approach to detect communication from pressure-transient data, and to quantify the magnitude of crossflow rates between reservoir zones. The formulation captures the influence of interference between wells caused by production. While complementing diagnostic information from other sources to confirm fluid movement from isolated zones, the method also quantifies the connectivity of the communicating media, and the amount of crossflow rates as a continuous function of time.