A Systematic Study of Different Delayed Systems for Mudcake Removal in High-Temperature Horizontal and Multilateral Wells

Abstract

AbstractEffective removal of drilling-mud filter cake during well completion is essential to reduce the formation damage caused by drilling activities in many production and injection wells. This task is very difficult to achieve, especially in horizontal/multilateral wells. Harsh chemical treatments (acids, oxidizers, and chelating agents) have been used extensively to conduct water-based mudcake cleanup treatments. However, these approaches have been limited due to the associated high corrosion rates and un-even mudcake removal. With their controlled reaction with the mudcake, mild chemical nature, better health, safety and environmental (HSE) profile, different acid-precursor systems provide an excellent alternative to harsh chemical treatments in high temperature formations.This work examines the efficiency of two acid-precursor systems to be used for mudcake removal in horizontal wells. These two acid-precursors (an ester of acetic and formic acid) will generate acid at slow rate at downhole conditions, resulting in uniform mudcake removal. The acid release rate of both in-situ acid generator systems was calculated at targeted average reservoir bottom-hole temperature of 130°F. The study was conducted at simulated reservoir conditions of 500 psi pressure for building the filter cake and 300 psi pressure for soaking the treatment. Drill-in fluids (DIF) sample collected from the field was used for conducting the filter cake removal tests. Return permeability experiments were performed using HPHT filter press cell.Filter cake removal efficiency of formate ester showed that this system removed 59.3 wt% water-based mudcake formed on a 5 μm ceramic disk when soaked for a prescribed period of 24 hours at 130°F and 300 psi nitrogen pressure. Similarly, filter cake removal efficiency of acetate ester tested on similar conditions removed 30.4 wt% of the filter cake. The break through time for the reactive fluid to penetrate through the mud filter cake was found to be approximately 15 hours for formate ester. Acetate aster system breakthrough was found to be nearly 7 days. Compared to acidic brine (1 wt% HCl), these systems will have slower fluid loss rates where the amounts of collected filtrate were found to be 14.6, 2.7, and 2.5 cm3 for 1 wt% HCl, formate ester and acetate ester, respectively, after soaking time of 2 hours.