A Comprehensive Model for Acid Stimulation of Lower Completions
Kristian Mogensen, Graham Edmonstone
Abstract
Abstract Long horizontal or highly deviated wells require lower completion liners to improve well and reservoir management of the carbonate reservoirs in ADNOC's portfolio. Optimum well productivity depends on effective stimulation post drilling. Traditionally, a complicating factor in a matrix-acid stimulation treatment has been poor control of the acid placement along the reservoir section to total depth (TD) without stage equipment or chemical diverters. The limited-entry liner (LEL) lower completion addresses the shortcomings of other stimulation techniques. It consists of a number of unevenly spaced holes with the purpose to distribute acid evenly along the reservoir section to be stimulated. ADNOC is planning to execute a series of pilots to test and possibly expand the operational envelope of the LEL technique. Design of a the hole-size distribution requires a mathematical model, which accounts for the various pressure drops encountered in the system as well as the impact of the chemical reaction between acid and rock. In this work, we present a comprehensive algorithm for designing a hole-size distribution which yields a user-specified acid coverage and also provides the best possible wormhole penetration, subject to a number of constraints related to surface pressure, pump rate, and acid volume available. We make use of findings published over the past 15 years in the SPE literature to arrive at an enhanced design philosophy, which is appropriate for the carbonate reservoirs in ADNOC's portfolio. The design model takes into account a number of important parameters, including fluid and reservoir properties, as well as completion information such as tubing ID, liner ID, and the LEL hole sizes. A check is made using nodal analysis software to ensure that the LEL completion does not act as a flow restriction during back-production.