A new generation Reservoir Drill-in Fluid (RDF) has been developed to mitigate the potential of damage to the producing formation and eliminate the need for post-completion cleanup.This RDF system was developed to perform synergistically where openhole gravel-packing or expandable screen completion styles are utilized. This new RDF system generates an active filter cake which is impermeable to aqueous fluids, thus reducing fluid loss into the producing formation. Concurrently, the now residual filter cake is permeable to formation hydrocarbons. This system utilizes organophilic components which generate preferential oil channels in the residual filter cake, thereby, eliminating the need for stimulation/cleanup from either internal or external chemical breakers. The preferential channels also help reduce the influx of aqueous formation and/or injection fluids. This paper details the development of the RDF system and the engineering of it on two openhole gravel-pack completions in the East Wilmington Field off the coast of Long Beach, California. It discusses the development of the system and the field trials. A maintenance schedule used by the fluid engineers for anticipated potential problems is also discussed. The field performance is discussed and lessons learned are contrasted with conceptual design. Comparative data from earlier horizontal wells are included and contrasted with respect to the RDF system design, drilling parameters and well start-up. Finally, the initial well-test data are presented. Introduction In wells that are completed with open gravel packs, particular attention and study has been given to effects of the filter cake deposited on the sandstone reservoir. Depending on the chemical and physical nature of the filter cake, there can be detrimental impairment to both the producing reservoir and to the devised completion.[1–6] One of the primary functions of a Reservoir Drill-In Fluid (RDF) filter cake is to minimize both the invasion of the fluid's filtrate and drill solids into the intended producing zone. The deposition of an impermeable filter cake is critical in various reservoirs that have openhole completions where damage to the formation cannot be by-passed by perforating. The reservoir drilling fluid filter cake should be strong enough to prevent losses and premature screen out during the gravel pack process. After the gravel packing of the well is completed, the removal of the filter cake is desired to prevent plugging of the gravel pack and the completion screen. In low pressure reservoirs, filtercake removal could be especially necessary to prevent completion blockage. The preferred method employed to clean up the drilling fluid filter cake has been the use of chemical breakers such as oxidizers, acid, enzymes, a chelating agent solution or a combination of the latter two. Placement techniques for chemical breakers have included both post-gravel-pack and during the gravel pack. When post-gravel-pack placement occurs, sometimes there may be difficulty in treating the entire filter cake causing only localize treatment. If the chemical breaker is added during the gravel-pack operation, there may be a risk of premature filtercake breakthrough which could prevent the well from being completely packed with sand. External filtercake stimulation may not effectively contact all of the filter cake resulting in patchy filtercake dissolution. Breakthrough of aggressive chemical treatments may cause the migration of fines and chemicals into the formation under high differential pressure conditions. It is against this background that a new type of Reservoir Drill-In Fluid was designed utilizing the concept of an active filter cake whereby cleanup is initiated by the oil produced out of the reservoir instead of an external means. This Active Filtercake System still deposits a protective barrier across the formation; but instead of using a conventional starch fluid-loss-control agent and conventional calcium carbonate bridging material, it uses hydrophobic components that produce an organophilic filter cake. This organophilic filter cake provides channels through which hydrocarbons are travel through the gravel and then through the completion hardware into the production tubulars. The overall objective of the Active Filtercake System is to be non-damaging to both the reservoir and the completion.

A new surfactant capable of providing stable emulsions to as low as a 20/80 oil/water ratio while still maintaining a continuous oil phase is now possible. The new surfactant works in a variety of brines allowing flexibility in formulations and applications. The high internal phase emulsion allows formulations of higher density with less total solids. These high internal phase emulsions are stable at high temperatures and provide manageable (adequate) low-end rheological properties suitable for drilling and completion applications. This system demonstrates relatively less syneresis than a conventional invert. Using a higher internal phase requires less oil and subsequently lowers costs both from initial base fluid cost and final disposal of the base fluid. This new surfactant can also be used to formulate systems for conventional alpha-beta gravel packing, whereby the rheology profile approaches Newtonian properties. This paper will detail the chemistry behind the new surfactant, initial laboratory assessments and the potential applications for this new technology.

An established non-biopolymer reservoir drill-in (NBRDF) system which was developed in very early 2000 for high-density drilling applications – approximately 11.5 to 17.5 lbm/gal – was recently improved to provide functionality in low-density drilling applications – as low as 9.5 lbm/gal. Global implementation of this system over the last several years has demonstrated not only flexibility with respect to drilling and completing in diverse reservoirs but also its application as a workover system. In addition, this system was recently optimized by incorporating compatible chemistry to mitigate atypical damage mechanisms. As such, several case histories are presented to demonstrate the system's broad functionality with respect to density, completion type, reservoir, and logistics, as well as its capacity to reduce near-wellbore/formation damage. This non-biopolymer reservoir drill-in fluid (NBRDF) system demonstrates relatively high tolerance to solids and reservoir fluids as well as ease of hydration when mixing on the rig. Routinely the hydraulics are consistent and predictable even as no biopolymer is utilized. This system is compatible with the incorporation of an inhibitor, specifically, a scale inhibitor to mitigate calcium carbonate and minor sulfate scaling. This system recently incorporated a sized calcinated magnesium compound (MC2) and sized magnesium complex (MC3) which promotes viscosity, specifically low-shear rate viscosity, at a lower density range that was not achievable before. The initial concepts of buoyancy of solids and the exclusion of a biopolymer as incorporated in relatively high-density brines formed the basis for the development of this system. These concepts are discussed first to provide a background for the preceding recent improvements and case histories. Each case history presents a different set of objectives whereby pre-planning assessments were implemented to address and mitigate perceived risks as related to the fluids. The methods employed include assessments for rheology, scaling, hydraulics, displacements, compatibility and formation damage. The drilling and completion results for these projects exhibit a wide range of applications as well as flexibility with respect to required density, completion hardware and reservoir type. The procedures utilized for each project are evaluated with respect to specific drilling and completion targets and include the iterations/modifications required; subsequently the field learnings are also discussed.

A novel reservoir drill-in fluid (RDF) has been developed that utilizes viscoelastic surfactants (VES) as the primary viscosifier and as a consequence, eliminates the need to use biopolymers for viscosity. Biopolymers have been the standard RDF viscosifier for a long time. They provide stable rheological properties required for drilling and completing the reservoir section, but they have been difficult to remove as very few chemical breakers can effectively destroy the polymer chain. The VES-based viscosifier can be easily removed by a variety of non-aqueous materials, including produced hydrocarbons making this new RDF a viable alternative for a variety of openhole completion projects, particularly low-temperature and injector applications. This new VES-based RDF system not only suspends soluble bridging material, but supplies the rheological properties necessary to transport cuttings out from the wellbore. Fluid-loss control is achieved with a novel polysaccharide starch that is compatible with the surfactant used in the system. With the addition of this particular starch, the VES-based RDF exhibits similar characteristics to a biopolymer-based RDF which also utilizes polysaccharides and soluble bridging agents, and is stable enough to withstand conventional water-based RDF contaminants. This paper will detail the laboratory phase involved in the development of this new system. The testing confirmed that the properties normally associated with conventional biopolymer-based RDF systems are also achieved with this innovative VES RDF system. Additional testing revealed solids contamination effects and the effect that the addition of lubricants had on this unique system. Further investigation will also show the effect of a water-based filter cake breaker system currently being used in completion operations. Results of return permeability testing will also be discussed in this paper. The development of this new RDF system showed that VES technology currently being applied in other aspects in oil and gas completion operations can now be applied in drilling the reservoir, and that this unique system can achieve the same functionality as conventional water-based RDF without the use of biopolymers. Introduction Biopolymers have been used extensively in reservoir drill-in fluids (RDF) to drill the reservoir sections in oil and gas wells. Either xanthan gum or scleroglucan have been used successfully in the majority of water-based RDFs to help transport drill cuttings out of the hole and to suspend solid material in the fluid system when velocities are low or when circulation comes to a halt (Zamora et al. 1993; Powell et al. 1991). Along with a starch and a soluble bridging material, the biopolymer becomes part of a filter cake whose function is to prevent invasion into a permeable formation. In several parts of the oil and gas industry there is the concern about the invasion or leak off of biopolymers into the reservoir causing impairment to production or injection (Audibert et al. 1999; Krilov et al. 1996; Dalmazzone et al. 2004). Several professional papers mention that this impairment is a result of the polymer molecule settling or being adsorbed on or into the reservoir rock pore spaces. It has also been argued that any formation damage caused by biopolymers can be mitigated with clean-up treatment or that the concentration of biopolymers in the drill-in fluids is small especially when used with the starch and bridging agents (Navarrete et al. 2000). The debate on the impact of biopolymers on reservoir impairment made it clear that an alternative viscosifier should be examined as a replacement for biopolymers in some RDFs.

An innovative surfactant chemistry in a nonaqueous system with an oil-to-water ratio (OWR) of 20/80 was effectively utilized for the first time to provide wellbore stability and run a sand-control screen in an openhole gravelpack completion. This novel type of invert emulsion system uses relatively higher aqueous internal phase, i.e., less than 50/50 OWR, which subsequently allows for a relatively higher density than the drilling fluid. More importantly this system is maintained as solids free and oil continuous.The increasing application of Inflow Control Devices/Intelligent Wellbore Systems and swellable elastomers as well as drilling longer intervals and their exposure to shale/sand dictates the use of compatible and solids-reduced invert systems to reduce the risk of an unsuccessful gravel placement treatment caused by shale swelling or plugging of sand control screens. This novel high-internal phase system provides flexibility for these types of completions. The use of the higher internal phase allows the formulation of oil-continuous solids-free systems while still achieving the required density necessary in solidsladen aqueous systems. This paper will focus on the selection of the 20/80 high-internal-phase system for this openhole completion, the upfront testing and planning for deployment. Discussion will also be provided with respect to the mixing of the system at the wellsite as well as the lessons learned.