The Kraken field development was planned and executed through several batch drilling and completion phases to allow a review of each phase and incorporate the lessons learned in the next phase. All producers were drilled with an oil-based reservoir drilling fluid (OB-RDF). The lower completion with shunted sand control screens was installed in conditioned OB-RDF, followed by displacements to water-based fluids after the packer was set. Gravel packing was performed with a visco-elastic surfactant fluid, and a breaker treatment was spotted across the open hole prior to isolating the open hole with a fluid loss control valve. This paper discusses the design, execution and evaluation of the lower completion phase for the development of the Kraken field in the North Sea. This includes detailed reservoir evaluation, methodology followed for sandface completion selection, steps taken to improve efficiency through lessons learned and continuously extend well lengths to be gravel packed in a low frac-window environment, and well performance results in this 24-well field development, with focus on the 7 out of 13 oil producers, detailing 3 of them.

Openhole gravel packing is one of the popular completion techniques in challenging, high-transmissibility reservoirs. Many of such wells are drilled with synthetic fluids and completed with either a single-or a two-trip technique.In single-trip approaches, the entire wellbore is displaced to water-based fluids before running screens and subsequent gravel packing. Although successful in some cases, this technique has been problematic in reactive-shale environments because of problems in screen installation to target depth, resulting from shale swelling and/or collapse. Such problems led operators to a twotrip approach in which a predrilled liner is installed in syntheticbased mud (SBM), displacements are performed to water-based fluids, and the screens are run in a solids-free (SF) water-basedfluids environment, followed by gravel packing. In recent years, another approach was introduced, in which the displacements to water-based fluids are performed after the screens are installed in conditioned mud and the packer is set, followed by gravel packing with a water-based fluid. Although this approach eliminates the difficulties associated with screen installation as well as allowing a single-trip completion (no predrilled liner), it cannot be used in cases where conditioning is impractical.In this paper, we present case histories where screens were installed after the open hole was displaced to a solids-free SBM and the cased hole was displaced to completion brine, and gravel packing was performed using a water-based carrier fluid. This approach provides a cost-effective alternative to displacement of the entire wellbore to SF-SBM as well as eliminating the risk of screen plugging, and it was implemented successfully on two oil producers in Oyo field. Details of design, execution, and evaluation for drilling and completion stages, as well as well productivity measures, are provided. Review of the Practices to DateMany of the deepwater developments in West Africa use SBMs for both upper hole and reservoir drilling, and almost all of them require some form of sand control, openhole gravel packing being one of the widely used techniques. Gravel packing in SBM environments evolved substantially over the years, with a variety of options that can be categorized on the basis of the type of carrier fluid used for gravel packing [note that the terms SBM and oil-based mud (OBM) are used interchangeably in the context of this paper].Oil-Based Carrier Fluid. In this approach, the screens are necessarily installed with oil-based fl uids in the entire wellbore, where the wellbore fl uids can be any combination of (a) conditioned SBM, (b) fresh SBM (no cuttings), and (c) SF-SBM or oil-based carrier fl uid. The conditioned-SBM approach requires that the mud be passed through shaker-screens of suffi ciently small openings to prevent plugging of sand-control screens during installation and subsequent operations. As such, the type of screens used in the completion (wire-wrap or premium/metal-mesh) and the size of screen openings, and t...

Summary At some stage after drilling to target depth and before pumping the gravel-packing treatment or before putting the well on production, the drilling fluid is typically displaced from the wellbore. Practices in the industry vary significantly depending on the primary drivers of the completion engineers, sometimes with undesirable results. Inefficient wellbore displacements can cause a variety of problems, including increased nonproductive time, reduced well productivity, and incomplete gravel packing through various mechanisms. In this paper, we detail our best practices to ensure efficient wellbore displacements for sand-control completions on the basis of learnings from more than 500 openhole completions throughout the world from 2013 through 2016. In the design phase, these involve various compatibility tests, some of which are not commonly performed, and/or potential problems that cannot be identified easily when they are performed using conventional test procedures. Additional considerations include the modeling of fluid/fluid displacements and determining the fluid properties, pump rates, and fluid volumes required for effective displacements in a given wellbore geometry and flow paths. On the rigsite, they involve several quality-control tests, some of which have not been implemented previously.

Summary Two key benefits of downhole-gauge (DHG)-data analysis are identifying and minimizing the root causes of any failures that might occur during gravel packing and calibrating or verifying friction-pressure data for gravel-placement simulations. Although downhole pressure and temperature gauges are used often in openhole gravel packing, and expertise in analyzing the data certainly exists in companies that routinely use DHGs, to our knowledge, there is no publication that comprehensively discusses the method of analysis. DHG-data analysis, in general, requires more information than the gauge data themselves. This includes logs, wellbore schematic, pumping schedule, fluid properties, return-flow measurements, daily rig reports, and data relevant to displacements. The objective of this paper is to provide guidelines for DHG-data analysis to completion engineers, who are not routinely involved and thus are not experts in such analysis, by detailing the factors that must be kept in mind, offering a method, and demonstrating this method with several examples.

Many of the water injectors in sand control environments are being completed as long open holes due to higher injectivities attainable with such completions. Although target rates may often be achieved without any cleanup chemicals in production wells, injection wells require filtercake cleanup, in cases where • producing the well prior to injection is not feasible or desirable, (e.g., limited storage capacity on the rig, or artificial lift requirements due to low pressure or injection into water leg) • injecting above frac pressure is either not feasible (e.g., very high frac pressures and pump limitations) or not acceptable (e.g., sweep efficiency, premature water breakthrough, uncontrolled fracture height growth).Although a large variety of filtercake cleanup techniques and chemistries are available in the industry, most of these solutions are effective in producers. As demonstrated through laboratory experiments, achieving consistently high injectivities requires removal of drill solids from the filtercake, through either dissolution (e.g., acid formulations utilizing HF) or effective displacement techniques that will not result in injection of these solids into the formation pore throats (SPE 77449). In addition, an effective filtercake removal (including drill solids) in long open holes without inducing high losses into the formation (so that the wash pipe can be pulled out and a mechanical fluid loss control valve can be activated) remained as a formidable challenge, which becomes even a bigger challenge in wells drilled with conventional oil based muds (OBM), particularly in reactive shale environments.In this paper, we present a novel technique that addresses these challenges, proven through field application on a standalone screen water injector in Nigeria. The technique involves displacement of OBM from openhole with a viscous spacer pill containing a demulsifier, followed by completion brine containing a mutual solvent to weaken the filtercake without attacking the bridging agents, subsequently performing a high rate viscous pill displacement to remove the external cake, and finally spotting a water-based self-destructive fluid loss control pill to control the losses while pulling the wash pipe. Laboratory testing for designing the displacement stages, field execution, and well performance evaluation are detailed.