Initial Open Hole Gravel Pack (OHGP) completions that have been installed in Greater Plutonio to date have all achieved complete annular packs and zero mechanical skin factors, resulting in well productivity indices that are significantly greater than expected. The success of the Greater Plutonio OHGP completions has been attributed primarily to the rigorous design and field application of the fluid systems used at all stages of the well from drilling the reservoir through to the gravel pack itself and subsequent completion. An integrated approach was adopted for the design of the fluid systems involving extensive formation damage and fluid compatibility testing. To translate the robust design into a fluid system which can be applied effectively in the field, a thorough, fit for purpose QA/QC system for all drilling and completion fluids was developed, requiring extensive fluids testing and reporting at the well site. The paper describes in detail the reservoir completion philosophy, drilling and completion fluids' systems and overall operational practices used in the Greater Plutonio OHGP completions. It also discusses the fluids design phase of the project and the QA/QC processes implemented in the field. Finally the paper presents the well productivity data from the wells completed to date. Introduction The Greater Plutonio Development is a 5 field deepwater project, located in Block 18, offshore Angola (Figure 1). All 43 planned development wells are subsea in water depths ranging from 1200 to 1500m. Of the 43 wells, 20 are producers and 23 are injectors. The development drilling programme began in 2005 with the aim of drilling and completing 15 wells prior to first oil in 2007. All the 5 fields produce from poorly consolidated Oligocene, turbidite reservoirs and consequently sand control is required in all development wells. Each of the 5 fields is composed of multiple stacked reservoirs separated by shales. The formation sands are high permeability (Kaverage between 800 to 1500md) with low viscosity oil (0.5 to 0.8 cP). GOR ranges from 700 to 1100 scf/stb. Formation Sand Particle Size Distribution Laser Particle Size (LPSA) and sieve analysis was performed on the whole core recovered from the exploration and appraisal wells. The results of the analysis conducted on these wells are summarized in Table 1. These results are typical of all producing formations in the Greater Plutonio Development. The LPSA data for the main reservoir, the Plutonio O73, are shown in Figure 2. The majority of the sands are well sorted with low fines content. There are however some poorly sorted sands with higher fines content which result in the Uniformity Coefficient (D40/D90) ranging from 2 to 16 and the fines content from 1 to 15%. Overall the formation sands are poor to well sorted with low to high fines content. This particle size distribution data (PSD) combined with the limited amount of whole core data available for 5 fields, required the selection of a sand control system capable of providing well bore stabilization in all production wells. Shale Characteristics The deepwater Angola fields are located in shallow, immature sediments which typically have reactive shales that are incompatible with water based fluids. The experiences from the analogue fields in the basin clearly demonstrate the reactivity of the shales. The initial Open Hole Gravel Pack (OHGP) wells in an offset Angola deepwater block, were drilled with oil based mud and the hole was displaced to brine prior to running screens 1. Significant problems were initially encountered running screens due to shale instability and as a result the current system in the offset block deploys the screens in oil based mud.

Summary Water injection into soft sand is a global industry challenge because of the complex problem of maintaining sustained water-injection rates into the desired reservoir. Drilling, cementing, and completion engineers are addressing each technical and operational aspect of water injectors, including cement isolation. Cement serves as a barrier during well construction through to post-abandonment. It contributes to ensuring that no out-of-zone water injection occurs because of flow behind casing. If water does go out of zone, new drilling hazards that are a result of water breaching and a loss of reservoir management will occur. At present, as far as we know, the industry does not have a systematic methodology for defining and verifying the required physical and mechanical properties of the cement to endure water-injection service and to retain its isolation capability during well life. Cement-integrity simulators (CISs) provide different answers, mainly because they all assume a different initial stress-state in the cement after hydration. As a consequence, a new CIS model that computes this stress state has been developed, along with a large-scale testing setup to validate its predictions. The new model incorporates key-design parameters of effective CIS models: (1) The initial stress state after cement hydration is computed; (2) varying loadings that the cement sheath is submitted to are simulated; (3) the elasticity, plasticity, and failure of materials are taken into account; (4) the simulations are fast enough to facilitate sensitivity analysis; and (5) the model outputs allow the visualization of cement integrity across the entire length of the cement sheath, adjacent to reservoirs and to seals. Parallel to the modeling work, a large-scale test apparatus was built to evaluate cement zonal isolation under water-injection pressure and temperature conditions. Its objective was to generate pressure and temperature cycles inside sections of cemented casing assemblies to replicate the conditions of pressure and temperature variations in a water-injection well. The results of the test confirmed the accuracy of the new CIS model. They also showed that cooling because of water injection had a bigger impact on cement integrity than increasing pressure. In addition, the results showed that microannulus generation had more effect than tensile cracking in terms of cement-barrier-permeability increase.

Water injection into soft sand is a global industry challenge due to the complex problem of maintaining sustained water injection rates into the desired reservoir. Drilling, Cementing and Completion engineers are addressing each technical and operational aspect of water injectors, including cement isolation. Cement serves as a barrier from well construction to post abandonment. It contributes to ensuring no out of zone water injection occurs due to flow behind casing. If water does go out of zone, new drilling hazards due to water breaching and loss of reservoir management will occur. At present, as far as we know, the industry does not have a systematic methodology for defining and verifying the required physical and mechanical properties of the cement to endure water injection service and retain its isolation capability during well life. Cement integrity simulators (CIS) provide different answers, mainly because they all assume a d ifferent initial stress state in the cement after hydration. As a consequence, a new CIS model that computes this stress state has been developed, along with a large scale testing setup to validate its predictions. The new model incorporates key design parameters of effective CIS models. 1) The initial stress state after cement hydration is computed; 2) Varying loadings the cement sheath is submitted to are simulated; 3) The elasticity, plasticity, and failure of materials is taken into account; 4) The simulations are fast enough to facilitate sensitivity analysis; 5) The model outputs allow visualization of cement integrity across the entire length of the cement sheath; adjacent to both reservoirs and seals. In parallel to the modelling work, a large-scale test apparatus was built to evaluate cement zonal isolation under water injection pressure and temperature conditions. Its objective was to generate pressure and temperature cycles inside sections of cemented casing assemblies to replicate the conditions of pressure and temperature variations in a water injection well. The results of the test confirmed the accuracy of the new CIS model. It also showed that cooling due to water injection had a bigger impact on cement integrity than increasing pressure. Additionally, it showed that micro-annulus generation had more effect than tensile cracking in terms of cement barrier permeability increase. Based on this work, cementing design workflow for zonal isolation of water injectors has been established. As injection pressure and temperature, rock properties, confinement pressure and completion type vary from well to well, zonal isolation for water injection wells must be designed on a case-by-case basis. New cementing workflows for water injection wells involve rigorous cement mechanical property testing and cement stress modelling.

The Greater Plutonio development, deepwater offshore Angola, is BP's largest subsea development. The "soft" rock reservoirs require sand-control completions that are some of the most complex and challenging in the world. A commonly accepted view is that effective sand-control can result in sacrificing well productivity; however, the 23 wells completed to date have broken that paradigm with world class results and the largest well potentials in the history of BP.All twelve deepwater production wells employed Open Hole Gravel Pack completions, achieving outstanding results and technical limit productivity along with exceptional mechanical reliability and integrity. From the first well, they have all shown zero formation damage, resulting in individual well potentials up to 80 MBD. To support this prolific production capability, effective voidage replacement has been essential. Therefore, the injection well completions were designed to deliver equivalent well performance, while still providing robust sand-control. Based on this, Cased Hole Frac-Pack completions were selected for the initial gas and dual service injection wells with Stand-Alone Screen completions for the water injectors. The injector completions were as successfully deployed as their producer counterparts with technical limit injectivity on all the wells, setting a new standard for flow efficiency in high transmissibility reservoirs and delivering some of the largest water injector completions in BP's portfolio.The Greater Plutonio completions excellence story is one of a truly performance driven and innovative team. Productivity indices are up to four times greater than prognosed and mechanical skins in production wells are all zero (compared with +5 to +20 in analogous fields). This is underpinned by comparable injection performance and furthermore, the over 99% mechanical reliability and full data acquisition uptimes have substantially reduced the probability of costly well interventions in the future. This paper discusses the keys to the successful delivery of this world class completions performance and covers best practices and resultant well performance data of the first 23 wells from the planned initial 43 subsea well development.

This paper presents the results of design and field execution of sand control completions for Raven High Pressure High Temperature (HPHT) gas field in Egypt. The reservoir contains stacked channel formation sands, that require sand control completions. The completions design is complicated due to combination of sand control and HPHT environment where industry has limited experience. The selected completions type was an Open Hole Gravel Pack (OHGP) with a pre-drilled liner. A series of lab testing has been conducted to design and qualify completions fluids. The lab test program included formation damage tests, shale stability tests under dynamic and static conditions, materials and fluids compatibility tests and others. The downhole completions hardware was specifically designed to allow effective displacement from oil based mud to completion brine fluid with subsequent gravel pack placement. The circulating gravel pack placement technique was selected using Cesium Formate brine as a gravel carrier fluid. The field installation campaign of the selected completions method is currently underway with 4 wells already successfully being completed. All completed wells demonstrated excellent well performance results with very low completions skin. The well flow-back and test results exceeded expectations, indicating the entire reservoir sand was contributing to flow, demonstrated greater than predicted Productivity Index (PI) with minimal skin damage. Sand control integrity was achieved with full gravel pack efficiency.