Use of Oil-Based Reservoir Drilling Fluids in Open-Hole Horizontal Gravel-Packed Completions: Damage Mechanisms and How to Avoid Them

Abstract

Open-hole horizontal wells are increasingly used to improve reservoir exploitation and production rates by targeting specific zones and maximizing reservoir exposure. The drilling fluid of choice in many of these wells is "oil based" due to enhanced drilling rates with minimized friction as well as improved wellbore stability. However, in horizontal wells requiring gravel packs, the industry in general has been reluctant to use OB reservoir drilling fluids (RDF) for various reasons. Because the gravel pack (GP) carrier fluids that have been successfully used to date are all water-based and the use of OB-RDF would necessitate displacement of open hole to WB fluids prior to GP, the practice has been to switch to WB-RDF once in the reservoir section. This was due to concerns as to adverse fluid-fluid interactions resulting in sludging and difficulty in maintaining filtercake integrity while displacing OB-RDF in the open hole, leading to complex fluid management issues. An additional factor has been the perception that WB-RDF filtercakes are easier to remove should it be necessary, since most commonly used cleanup chemicals are water-based and the weighting/bridging agents used in the RDF are also water-wet if the RDF is water-based. In this paper, we present results from experiments conducted with OB-RDFs in the presence of gravel packs. We investigate two scenarios:the gravel pack carrier fluid is water-based, andthe gravel-pack carrier fluid is oil-based. In the first case, provided that no sludges are formed during displacement to water-based fluids, the retained permeabilities are comparable to or better than those obtained with WB-RDFs, although values lower than 0.04% can be expected in the presence of sludging. Another issue relevant to gravel packing wells drilled with OB-RDFs is the yield strength of their filtercakes in comparison to WB-RDFs. It is found through yield stress measurements of various RDF cakes that OB-RDFs have several orders of magnitude lower yield strength than their WB counterparts. This finding is consistent with the reported lower flow initiation pressures for OB-RDFs, and indicates that cake erosion during gravel packing is more likely with OB-RDFs. In order to optimize the sequence of fluids to obtain a good displacement of the RDF at field scale, we use a purpose-built numerical simulator. This simulator is a fluids mechanics code that can accurately calculate displacement fronts in field conditions: eccentric deviated annulus with as many fluids as necessary. Its main use is to detect unstable displacements such as channeling of the displacing fluid on the wide side of the annulus or slumping in horizontal portions. Furthermore, we provide data on a new oil-based gravel pack carrier fluid that can be used to eliminate fluid incompatibility and fluid management issues associated with the switch from OB to WB fluids. The laboratory and large-scale yard test results are presented, addressing critical considerations for oil-based GP carrier fluids. It is found that such emulsion systems can thicken or break (depending on the emulsifier concentration) at high shear rates unless the emulsion is made at the highest shear that it will be exposed to. The implications of these results on field practices are discussed along with recommendations on avoiding damage in gravel packed wells drilled with oil-based RDFs.

A Review of Water Reduction Techniques for Open Hole Gravel Pack Completions

“…Higher drawdown imposed on the well not only increases the motive force pulling liquid up and around the plug, Ladva et al 2001 5 showed that it can also cause channels to form in the gravel pack, as particles are forced together by high volumes of water expanding upward. It is unclear how long these channels can persist in the gravel pack once they have been formed.…”

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

“…The software applied the well geometry, fluids density and rheology data to generate different fluids flow/interface profile at specific pump rates. Previous industry experience had identified the need for contrasts between the mechanical properties of fluid being displaced and the displacement fluid to enhance wellbore fluids clean out 27,28 . A base case model was developed using a spacer fluid system, i.e., base oil, weighted/viscous spacer (push pill) and a low weight cleaning/wash pill, which was a blend of brine and surfactants, Figs.…”

Open-Hole Horizontal Drilling and Gravel-Packing With Oil-Based Fluids - An Industry Milestone

“…The fluid needs to be stable until the gravel placement is completed and the open hole is isolated through a mechanical fluid loss control device. It must however phase separate, before the well is put on production, for two reasons: (a) broken fluid will facilitate flow back: this is not as critical in oil wells as it is in gas wells, since dilution of the emulsion through produced oil reduces the carrier fluid viscosity, 14 and (b) phase separation is critical for the reversal of filtercake wettability and dissolution of the CaCO 3 bridging agents in the cake. After extensive experiments, involving phase separation tests as well as cake reversibility and carbonate dissolution tests, the composition of the fluid for the particular field conditions has been finalized as: 28% base oil, 2% emulsifier, 50% 10.8-ppg NaBr brine and 20% CAS, with a carrier fluid density of 9.4-ppg.…”

“…Although there are several recent techniques that allow water-based gravel packing of wells drilled with S/OB fluids with a single trip approach, the potential of reactive shales mixing with gravel during the packing process as well as potential damage in water-sensitive formations (in the event that the carrier fluid is lost into the formation due to cake erosion/lift-off) remain as valid concerns. The oil-based gravel packing fluid detailed in earlier publications [11][12][13][14] addresses the concerns with regard to reactive shales as well as eliminating the requirement for a two-trip approach, saving valuable rig time and providing means for an all-oil drilling and completion system.…”