This study presents a 3D analytical model to analyze the transient flow into multilateral horizontal wells. The model considers arbitrary phasing angle, selective lateral completion, non-uniform formation damage around each lateral, and areal and vertical permeability anisotropy. Using the model, transient pressure, derivative, and rate distribution characteristics of multilateral horizontal wells are investigated. Flow regimes are examined. Asymptotic approximations for each flow regime and pseudoskin equation are provided.

A sensitivity study is carried out to identify the parameters controlling the transient pressure, derivative, and fractional rate responses. The sensitivity study includes the impact of lateral length, orientation, and number, formation anisotropy, and the degree of formation damage around the laterals. If all the laterals are put on production during the test, it is almost impossible to estimate principal permeabilities, their directions, and skin factors around each lateral by examining transient pressure and derivative responses only. When all the branches produce, the transient rate distribution is strongly controlled by the skin due to formation damage. Therefore, if transient rate distribution data, as well as the pressure, is recorded during the test, non-uniqueness in the interpretation of test data may be minimized. Although it is more expensive and time consuming, testing each lateral individually may provide more reliable estimates of formation properties and damage.

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