Formation Damage: A Novel Approach in Evaluating Zonal-Productivity Loss

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 177533, “Formation Damage: A Novel Approach To Evaluate Zonal-Productivity Loss in Horizontal Wells,” by C.B. Maalouf, I. Baca Espinoza, S.M. Al-Jaberi, J.Y. Marrauld, and M. Amer, Abu Dhabi Marine Operating Company, prepared for the 2015 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 9–12 November. The paper has not been peer reviewed. The paper describes a novel methodology to construct distributed formation damage across openhole wells in carbonate reservoirs and to evaluate the effects of damage on zonal productivity. This methodology improves the prediction of well productivity by identifying the contribution of various types of damage to zonal productivity. This is critical for efficient decision making concerning well-completion and field-development options, particularly at the early stages of greenfield development. Introduction Numerous papers have investigated near-wellbore damage caused by drilling and acid, but the majority of these studies assume a homogeneous anisotropic reservoir and a perfectly horizontal well with constant diameter. In practice, these assumptions are unrealistic, especially when dealing with multi layered carbonate reservoirs. The proposed methodology in this paper relies on more-realistic assumptions made on the basis of actual well and reservoir data. The case presented in this study involves a horizontal openhole well drilled across a multilayered oil-wet carbonate reservoir of a greenfield, with baffles and barriers present between reservoir layers. The study evaluates the damage types experienced by the formation and their effect on productivity. A discussion of formation damage, including the mathematical bases of the skin concept, geometrical skin, drilling-induced skin, and the productivity index (PI) of a horizontal well, is included in the complete paper. Evaluation Methodology On the basis of the equations provided in the complete paper, a well model was built to evaluate the PI of a horizontal well. The proposed method requires two steps. The first step is to evaluate the well damage after drilling. To do so, a production test should be performed and bottomhole flowing pressure recorded. By analyzing the bottomhole pressure-transient behavior, the flow regime can be identified. Then, the average damage skin around the wellbore can be obtained, depending on the flow regime. Also, a production-logging-tool (PLT) acquisition should be performed across the entire drain in order to estimate zonal productivity. The model is then matched with PLT data by iteration over the damaged-zone permeability. With the distributed damage permeability per zone obtained from the model, the skin can be calculated. Here, it should be noted that the caliper data after drilling should be used to account for the geometrical skin created by drilling-induced washouts.