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...
Gravel-packed wells in the "C" field located in offshore Angola are prone to damage by a variety of factors including scales, fines migration, paraffin and asphaltene deposition resulting in skin values of 45-95. This paper focuses on the approach used for 2 subsea open hole gravel packed wells located within "C" field. Rigless subsea stimulations in approximately 470 m of water using an intervention vessel with the downline deployed via the vessel moonpool. Additionally, a stimulation vessel was utilized to provide pumping and fluid capacity without disturbing the primary intervention operations. This paper documents the efforts made to restore the wells forecasted production by bullheading the acid stimulation treatment from the stimulation vessel through the open-water hydraulic access system installed on the intervention vessel. Well history attributes the impairment to fines migration accumulation and scale and paraffins deposition. The proposed stimulation fluids were designed to treat as many damage mechanisms as possible during a single intervention. The basis for design incorporated a primary solvent pre-flush to clean possible paraffin and asphaltene deposition as well as prepare the reservoir and proppant pack for further stimulation fluids by stripping away hydrocarbon residue. The preflush was followed by a second treatment fluid consisting of HCl acid to remove any carbonate-based damage. The final treatment fluid utilizing a combination of HCl acid and hydrofluoric acid (HF) was specifically designed to remove fines contained in the gravel pack and screens. Injectivity tests were performed to evaluate the reservoir prior to and after the acid treatment as well as to help understand the damage mechanism. Based on the bottomhole pressure response during acid-treatment stages, measurable improvements were evident on both wells, which supports the pre-treatment damage diagnosis. The efficient and cost-effective execution of the treatment campaign, combined with the conclusive post-stimulation production data, confirms the effectiveness of open-water hydraulic access by utilizing an intervention vessel and a stimulation vessel, allowing to provide pumping and fluid capacity without disturbing the primary intervention operations on complex subsea wells. Post-stimulation results after the successful removal of wellbore scale and formation damage in the two subsea wells showed an average increase in oil production of 60%. Skin damage was reduced by 66% on Well A and a complete removal of skin on Well B. The results confirm the effectiveness of cost-driven acid stimulations on complex subsea wells without the use of a drilling rig as well as demonstrating the ability to address multiple damage mechanisms from a single intervention.
Summary Most of the deepwater reservoirs in Angola are weakly consolidated sands, requiring sand control, and openhole gravel packing is one of the most widely used sand-control techniques for producers; Block 15/06 is no exception (Hecker et al. 2004; Whaley et al. 2007; Pena et al. 2013; Menezes et al. 2013; Bingyu et al. 2016). High-inclination wells targeting multiple reservoir sections interlayered with reactive shales, relatively low fracture window, and prolonged well suspension without well cleanup were some of the challenges that needed to be addressed to ensure completion integrity and well productivity. This paper presents the measures taken during the design and execution phases to address the project challenges, along with an evaluation of completion integrity and well performance. Analysis of the downhole-gauge data is detailed for one of the wells as an example, illustrating the importance of downhole gauges in the completion.
Most of the deep water reservoirs in Angola are weakly consolidated sands, requiring sand control, and openhole gravel packing is one of the most widely used sand control techniques in the area, Block 15/06 being no exception. High inclination wells targeting multiple reservoir sections interlayered with reactive shales, relatively low frac window, and prolonged well suspension without well cleanup were some of the challenges that needed to be addressed to ensure completion integrity and well productivity. This paper presents the measures taken during the design and execution phases to address the project challenges, along with an evaluation of completion integrity and well performance. Analysis of the downhole gauge data is detailed for one of the wells as an example, illustrating the importance of including downhole gauges in the completion.
Openhole gravel packing is a popular completion technique 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-base fluids before running screens and subsequent gravel packing. Although successful in some cases, this technique has been problematic in reactive shale environments, due to problems in screen installation to target depth, resulting from shale swelling and/or collapse. Such problems led operators to a two-trip approach, where a predrilled liner is installed in synthetic-base mud (SBM), displacements performed to water-base fluids and the screens are run in solids-free water-base fluids environment, followed by gravel packing. In recent years, another approach was introduced, in which the displacements to water-base fluids are performed after the screens are installed in conditioned mud and the packer is set, followed by gravel packing with a water-base 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 openhole was displaced to a solids-free SBM and cased hole to completion brine, and gravel packing was performed using a water-base carrier fluid. This approach provides a cost-effective alternative to displacement of the entire wellbore to solids-free SBM as well as eliminating the risk of screen plugging, and was successfully implemented 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, along with a discussion of a continuous circulation device successfully used during drilling.
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