Guidelines for Shale Inhibition During Openhole Gravel Packing With Water-Based Fluids

Abstract

Many of the problems associated with the use of water based fluids in drilling and completion operations are caused by incompatibilities between the fluids and the shales. Such incompatibilities may result in washouts, increased drilling costs (solids handling, rig time, dilution fluids, dilution fluids), shale sloughing during the drilling operation and during the drilling operation and after displacements to solids-free completion completion fluids or during gravel packing. One of the most important factors leading to an undesired result (either a premature screenout, thus a potential sand control failure, or a higher skin) in water-packing of open holes is the presence of reactive shales in the interval to be gravel packed. Although there is a substantial amount of literature on shale inhibition with water-based drilling fluids, the importance of shale inhibition and the problems associated with shale reactivity during gravel packing remain largely unexplored. Furthermore, shale inhibitor selection often relies purely on a comparison of the results from bottle roll tests using shale samples in candidate fluid/inhibitor pairs (drilling or completion fluid) and on tests measuring degree of shale swelling. While these tests are highly functional, they can only provide information on the relative performance of fluids, and their relevance to gravel packing is questionable, as these tests do not simulate the conditions experienced during such treatments. This paper presents guidelines on selection methodology of shale inhibitors for use in gravel packing applications based on the data available in our respective companies, including a comparison of results from conventional bottle roll tests to those from flow through predrilled holes in shale core samples. Recommendations are made depending on brine type and density, type of shale, temperature, fluid exposure history, as well as environmental considerations. Introduction Openhole horizontal completions have emerged as a cost-effective means of exploiting deepwater reservoirs, many of which require sand control. Gravel packing is the preferred sand control technique for such environments where remedial treatment costs are prohibitively high.1 Two techniques have been employed for gravel packing open holes with varying degrees of success: alternate path and water-packing. The focus of this paper will be to address one of the problems considered to be a key risk factor in successful implementation of water pack treatments. The risks associated with open hole openhole water packing treatments completions completions can be summarized as:Swabbing, which has been addressed through the development of antiswab tool systems,2Exceeding fracturing pressureduring the beta wave, which has been addressed with the development of beta wave attenuators3 or use of low density gravel allowing lower pump rates without the concern for gravel settling in the work string,4during the alpha wave in environments with narrow frac window, which in some cases may be addressed through the use of low density gravel,4Filtercake erosion, which remains as the biggest uncertainty,5Reactive shales which may either collapse/slough or disperse in the carrier fluid; the former may lead to a premature screenout due to blockage of the annulus and the latter may result in a low permeability gravel pack due to shale and gravel intermixing.5–8

The Evolution of Sand Control Completion Practices for the Enfield Deep Water Development

“…A dynamic testing technique (Shenoy et al, 2006) confirmed that the shales tested were not significantly sensitive to correctly formulated water based fluids of the type being used. Although the shales were found to be much less reactive than feared, it was concluded that glycol inhibition was sub-optimal in the RDF used for both ENA01 and ENA02H.…”