Filtercake Cleanup in Open-Hole Gravel-Packed Completions: A Necessity or a Myth?

Abstract

Offshore reservoirs requiring sand control pose a major completion challenge because of extremely high cost and risk involved in remedial treatments, particularly in sub-sea completion and/or deep-water environments. It is therefore of utmost importance to ensure sand control without sacrificing flow conformance, recoverable reserves and well deliverability throughout the expected life of the completion. A major trend in these environments is towards open-hole, horizontal, gravel-packed completions. Although gravel packing stabilizes the wellbore, it can also entrap the filter-cake formed by the reservoir drilling fluid, potentially resulting in high drawdown requirements (flow initiation pressures) and/or low production rates (retained permeabilities). The cleanup procedures in the industry have varied significantly from no cleanup at all to complicated two-stage breaker treatments involving post-completion coiled tubing intervention, with no guidelines existing in the literature. In this paper, we present experimental results and field cases involving filter-cake flow-back through gravel packs with and without cleanup. Effects of various parameters, including gravel size (40/60, 20/40, and 12/20), formation permeability, drill-solids type (clays, quartz) and concentration, and the type of cleanup fluid have been investigated. Flow initiation pressure and retained permeabilities during flow back are reported as a function of these parameters. The experimental results show that the flow initiation pressure is a strong function of gravel size and the type of drill solids. It is concluded that, in clean (low-to-no clay content) formations of large grains and high permeabilities (~ several darcies) requiring large gravel sizes (e.g., 12/20), an enzyme or an oxidizer treatment is sufficient based on laboratory results and productivity predictions. This conclusion is also supported by several field applications as shown. In lower permeability (~ 100–250 md) formations of small sand sizes requiring smaller gravel (e.g., 40/60) elimination of both the fluid loss control agent (starch) and bridging agent (CaCO3) is necessary based on high flow initiation pressures and low retained permeabilities. In intermediate permeability (~ 500–800 md) formations of medium size sand-grains typically requiring 20/40 gravel, the results depend strongly on the type of drill solids: in clean formations (no clays in drilling fluid), an enzyme or an oxidizer treatment is sufficient, while in dirty formations removal of both CaCO3 and starch is necessary. These results are also supported by field case histories presented in the paper. Introduction Gravel packing has been gaining wider popularity in open-hole horizontal completions where sand control is required, particularly in sub-sea completion and/or deep-water environment. The cost of intervention in such cases makes risk mitigation a much more pronounced task. Until recently, a large majority of horizontal sand control completions have utilized standalone screens. However, because a substantial fraction of these wells have failed prematurely (either productivity loss due to screen plugging or loss of sand control due to screen erosion),1 many operators have changed their primary completion technique in these wells from standalone screens to gravel packing. This is particularly true in formations containing a large fraction of non-pay (shale, mudstone/siltstone) and/or have a wide particle size distribution.2

Novel Filter Cake Breaker Design and Successful Use for OHGP Carrier Fluid

“…As the costs associated with filter cake cleanup treatments during completion stage are typically marginal compared to potential intervention costs, a thorough cleanup treatment is considered an integral part of the completion operations in majority of OHGP wells in order to maximize well productivity and longevity (Brady et al, 2000). A filter cake trapped by the gravel can result in high drawdown requirements, non-uniform inflow profile, and/or low productivity (Tiffin et al, 2001, Hodge et al, 2010.…”

“…A filter cake trapped by the gravel can result in high drawdown requirements, non-uniform inflow profile, and/or low productivity (Tiffin et al, 2001, Hodge et al, 2010. Therefore, cleanup treatments designed to degrade/remove filter cake can reduce the potential productivity impairment, reduce the flow initiation pressure for open-hole gravel packs (Hodge et al, 2010), and provide more uniform production profile and avoid premature water or gas breakthrough (Brady et al, 2000).…”

“…Modern techniques involve incorporating breakers into the gravel-pack carrier fluid to place the cake-breaking chemicals into the wellbore during gravel packing operations (Brady et al, 2000). Incorporating breakers in GPCFs to attack the filter cake offers several advantages.…”

Evaluation of Nonreactive Aqueous Spacer Fluids for Oil-based Mud Displacement in Open Hole Horizontal Wells

“…An effective cleanup treatment delivers optimum life cycle productivity by allowing access to the entire payzone, minimum drawdown pressure across the reservoir and therefore, lowers the risk of early water breakthrough and fines migration 3 . Uniform placement and complete treatment of horizontal wellbore with conventional breaker fluids is difficult to achieve, especially in high-permeability sandstone reservoirs because of the rapid fluids reaction and leak off at the first point of contact.…”

Laboratory Evaluation of RDF Breakers Under Linear and Radial Flow Conditions

“…Since the early 90's, a significant effort has been devoted to understanding the damage mechanisms associated with Reservoir Drill-in Fluids (RDF), and to develop breaker systems to specifically target bio-polymers and bridging agents in the RDF cake for improved wellbore clean-up (Almond et al, 1995, Burnett, 1998Zain et al, 1999;Brady et al, 2000a;Luyster et al, 2000;Brannon et al 2003;Ali et al, 2004;Al-Otaini et al, 2005;Battistel et al, 2005;Nasr-El-Din et al, 2005, 2007Siddiqui et al, 2006;Samuel et al, 2009). Open hole wellbore clean-up techniques include inorganic acids, strongly buffered acids, chelating agents, oxidizing agents, enzymes, delayed release organic acids and combinations thereof.…”