Openhole Cleanup of Deep, High-Temperature Horizontal Wells With a Chelant-Based Acid System—Case Histories From Indonesia

This mud typically contains XC-polymer, starch, polyanionic cellulose, and a relatively small amount of calcium carbonate particles, and is used to drill a deep sandstone reservoir (310°F). Calcium carbonate particles are frequently used as weighting material to maintain the pressure that is required for well control and minimize the leak-off. Such solids become consolidated and trapped in the polymeric material and this makes the filter cake a strong permeability barrier. The conventional method for cleaning the filter cake is by circulating solid-free formate brines at a high flow rate. This mechanical technique removes only the external drilling fluid damage. Citric acid at 10 wt%, formic acid, and lactic acid were found to be incompatible with formate brine at room temperature. However, these acids were compatible with formate brine at temperatures greater than 122°F. Only acetic acid was compatible with formate brine. A formula was developed that is compatible at room and reservoir temperature. This formula was effective in removing filter cake. A corrosion inhibitor was added to protect downhole tubulars. In general detail, this research will discuss the development of this formula and all tests that led to its development.

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Strategies for Removal of Formate Brine-Based Drill in Fluid (DIF) Filtercake in Gravel-Packed Completions: A Laboratory Evaluation

Salgaonkar

Ali

Danait

et al. 2010

International Oil and Gas Conference and Exhibition in China

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Formate brines and drilling fluids were primarily developed for high pressure drilling and completion applications. This completion fluid system is now being employed in more benign pressure environments and also to drill and complete formations with specific properties. This was the case where a potassium formate brine with 1.25 specific gravity (S.G.) was specified as the base fluid for the drill-in fluid (DIF) as well as completion brine for several openhole completions requiring gravel packing in offshore Brunei. The DIF used to drill the open hole deposits a protective filtercake on the borehole wall that is typically removed by means of a suitable removal system, enabling undamaged production. Openhole filtercake breaker systems that are typically employed range from mineral and organic acids, which aggressively attack the filtercake and result in an incomplete cake removal, to ortho-esters, which hydrolyze in the brine and lead to the formation of a delayed acid, which has proven more efficient. The ortho-esters are mixed in the base brine and placed inside the open hole or gravel pack and allowed to react over time. Formate brines, however, have proven to be poor base fluids for the ortho-esters because of their inherently high pH. A laboratory evaluation was conducted to address this problem. The tests showed that these ortho-ester-based systems, when mixed in a potassium chloride or sodium-bromide brine system, can be employed to break the formate-based DIF filtercake. A chelant-based breaker system, however, provides the most efficient cleanup with the necessary delay. This paper addresses the challenges and details of the laboratory testing performed to arrive at an optimized chelant-based delayed-breaker system in formate brine for removal of formate-based filtercakes. The paper also presents results of the performance of the ortho-ester system.

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Openhole Cleanup of Deep, High-Temperature Horizontal Wells With a Chelant-Based Acid System—Case Histories From Indonesia

Abstract: TX 75083-3836, U.S.A., fax 01-972-952-9435. Abstract

Cited by 3 publications

References 10 publications

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Characteristics and Removal of Filter Cake Formed by Formate-Based Drilling Mud

Strategies for Removal of Formate Brine-Based Drill in Fluid (DIF) Filtercake in Gravel-Packed Completions: A Laboratory Evaluation

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