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Abstract The Hibiscus field situated off the North coast of Trinidad is a large, stratigraphically isolated and well-connected gas field which has 14 years of production history. Notwithstanding this extensive production history and overall recovery, a number of key subsurface uncertainties have been identified. The scope of this study was to better understand reservoir complexity and define subsurface risk and opportunity. An integrated and iterative multidisciplinary approach to reservoir modelling was applied in an effort to meet these objectives. A modern suite of workflows such as Monte Carlo Petrophysical analysis, conditioning of models to seismic attributes, experimental design based uncertainty analysis and assisted history matching were used to generate new static and dynamic reservoir models. The key aspect of this workflow was 20+ major static to dynamic model iterations and a large number of deterministic simulations to rank and asses the validity of static concepts. The learnings were subsequently applied to create a robust reference case, static and dynamic uncertainties framed and a static probabilistic uncertainty workflow developed to QC the deterministic case. A full probabilistic assisted history matching exercise on the dynamic model enabled a refinement of the volumetric ranges and provided critical insight through analysis of posterior uncertainty distributions. The iterative workflow allowed concepts to be validated dynamically and it was demonstrated that high quality history matches could be achieved even after the removal of almost all dynamic multipliers – a common issue in simulation models. Significant improvements to pore volume distribution, the use of geologically derived dynamic baffles, and permeability distributions were amongst the key learnings on the static side. The probabilistic dynamic modelling was characterized by a strong GIIP convergence with a reduction of history match error, resulting in a refined volumetric range and better characterization of uncertainty ranges through posterior analysis. The application of modern integrated and iterative workflows to a mature field has better defined uncertainty ranges, understanding of reservoir behavior and overall resulted in a more robust suite of models. Key learnings identified were highlighted to support future reservoir model rebuilds. Ultimately this process has demonstrated the value of revisiting existing datasets in late life assets by generating higher confidence in remaining reserve estimates and business plan forecasts.
Folefac, A. (British Gas, Trinidad & Tobago Ltd.) | Hylkema, H. (Eclipse Petroleum Technology Ltd.) | Mason, S. (Schlumberger) | Graham, A. (Schlumberger) | Svoboda, C. (M-I) | Guzman, J. (M-I) | McCartney, R. (M-I) | Patey, I. (Corex UK Ltd.)
Abstract This paper summarizes the systematic methodology & engineering process employed to identify and refine the highly effective fluid-train solutions used to drill, and install the highly productive, long horizontal gas well completions of the NCMA Hibiscus Project offshore Trinidad. It presents and discusses the unique fluids design, pre-project evaluation, and the integrated application efforts undertaken to:Minimize formation and completion damage; and Maximize gravel-pack placement and filtercake removal efficiencies. The paper will identify important reservoir drilling and completion fluid service integration points (metrics), laboratory validation methods employed, and provide completion process details that led to the successful high-rate gas well installations in an unconsolidated sandstone reservoir. Specific topics discussed will include: the design and implementation of: the optimized Reservoir Drilling Fluid (RDF), RDF to Completion Fluid displacement, gravelpacking process, and the filtercake removal treatment. Finally, the paper will present case histories of the five completions installed in the Hibiscus reservoir and provide comparisons of:RDF drilling performance, gravelpacking efficiency, and well performance (productivity) of a stand-alone screen completion versus the gravel packed wellscreen completions that employed the unique RDF and filtercake cleanup treatments. Introduction Project Background The North Coast Marine Area (NCMA) lays North-northwest of Trinidad. (Figure 1) The original Hibiscus gas field development plan comprised a nine-well drilling campaign, utilizing a Minimum-Area Self-Elevating (MASE) rig aboard the Hibiscus platform. As a result of the high deliverability the first development phase was concluded after completing seven wells. Hibiscus was a "fast-track" gas development with the first completion to be installed less than 16 months after project sanction. First gas was required in July of 2002 at full contractual rates of 240 MMcfd/d. Initial well deliverability modeling predicted that a minimum of 4 horizontal wells would be required to meet this demand. The modeling suggested that the producing intervals in these wells would need to be 8.5" in diameter and between 1500 and 2000 ft in length to effectively exploit the reserves and meet the delivery requirements. The basis of design for the project imposed zero sand-production tolerance on the processing facilities. Although this permitted more economic design of the production facilities, it placed considerable emphasis on installing effective sand control. Geological Description of the Reservoir Reservoir formations in the Hibiscus field of the NCMA consist primarily of unconsolidated sand with interstitial clays and interbedded shales. The lithology of these formations is that of sandy, mixed and muddy turbidites. Extensive core and formation analyses including CAT-scan, XRD, granulometry, Hg porosimetry, and SEM micro structure were performed to characterize the rock and understand the potential damage mechanisms that might impact the target sands. This work indicated that the average clay & shale content ranges from approximately 7 to 10% with distribution being primarily intergranular, with occasional shale streaks. Porosity in these sands ranges from 10 to 21% with permeability from 10md to 1.0 Darcy. The average permeability is approximately 125 md. The net to gross for the Hibiscus wells was estimated to range from 75 to 100%. Granulometry of the prospective producing sands indicated that the uniformity coefficient (d40/d90) varied from 2.2 to as high as 16.4 with d90 values as low as 5μ.
Abstract With sand control being an issue for many operators; there is a prevalence of Open Hole Gravel Pack (OHGP) completions used in offshore reservoirs. Gravel packing is an industry recognized method of stabilizing the well bore and controlling sand in gas and oil producing wells. But while ensuring the longevity of the well it also entraps the filter cake formed by the reservoir drilling and completion fluids. These factors result in a lower production rate well and the need for higher drawdown. Therefore it is essential that the filter cake be removed along the length of the wellbore to ensure no unnecessary restrictions to production. This process requires an integrated approach to well start-up. It begins with the completion fluid used and ends with the start-up/bean-up procedure. The completion fluid type is essential in determining the lift-off pressure required by the filter cake. This pressure needs to be accounted for by the start-up rates used. Subsequently this start-up rate must be achieved in a safe and timely manner to ensure that the completion is not compromised, via the bean-up procedure. This necessitates the need for synergy between Subsurface, Well Engineering and Operations departments. The North Coast Marine Area (NCMA) operated by BG Trinidad and Tobago consists of 17 horizontal OGHP gas production wells; hence it is imperative that a well thought out start-up philosophy to ensure well productivity. The sands, which these wells are completed in, are characterized by their thin laterally extensive nature. These sands show relatively homogenous reservoir quality profile with good lateral connectivity. Currently NCMA produces from the M2, M4 and M6 packages, each with a NTG over 95%. These wells have been drilled in three phases over the past decade, the last being October 2009 to March 2010. This paper describes these improvements, challenges to the program and attempts to examine the results to determine any relative gains in productivity of the wells.
Abstract This paper describes the integrated approach adopted to optimize the gravel pack completion design and fluid selection for the North Coast Marine Area (NCMA) development project, offshore Trinidad. This resulted in the development of a uniquely engineered gravel pack completion design and associated procedures, incorporating a number of novel fluid-related and equipment technologies. Key challenges to the project were: wellbore stability, due to narrow mud weight windows and shale reactivity; effective sand control; productivity; and minimal rig space, leading to an ‘intervention less completion design’ philosophy, and an accelerated project schedule. These challenges are interdependent and rely heavily on fluid selection and optimization, not only for drilling operations but also for gravel packing and clean-up operations. Through effective tendering and subsequent teamwork, the completion design has resulted in high productivities and cost savings amounting to some US$ 5.5 million. Introduction The North Coast Marine Area (NCMA/Fig. 1) Hibiscus development consists of a nine-well drilling campaign, utilising a Minimum Area Self Elevating (MASE) rig on top of the Hibiscus Platform. Hibiscus was a "fast track" development with first gas less than 16 months after project sanction. The Basis of Design, developed during the front-end engineering design phase, imposed a zero sand tolerance for the processing facilities, allowing economic benefits for the production facilities but placing considerable emphasis on effective sand control. The design and installation of the sand face completion was crucial to provide effective sand control whilst maximising productivity to achieve an extended gas production plateau. Gravel packing was selected as the preferred method of sand control. Key to the success of the project was controlling formation damage. Extensive laboratory-based core studies were undertaken, at reservoir conditions, to identify potential formation-damage mechanisms. Sequence testing was employed to investigate each phase of the drilling, gravel pack and completion operation and the interdependency of the resulting formation-damage mechanisms. This was essential in understanding the total system behaviour and to optimize fluid selection. All testing was performed using representative core and formation brine from the Hibiscus MIV reservoir unit. Project Outline The Hibiscus development project was formally sanctioned in June 2000. The Well Engineering Project Team was established and in place in September 2000, with the operations team in the country in May 2001. The start of operations was determined to be early October 2001 with installation of the jacket and topsides followed by the installation and commissioning of the MASE-type platform drilling rig. A first gas requirement was set for July 2002 at full contractual rates of 285 MMscf/d. Initial well deliverability modeling predicted that a minimum of four wells would be required to meet this demand. This schedule implied that the first reservoir section would have to be drilled by December 2001, this schedule provided just over one year to tender for the fluids contract and fully design, develop and test the completion fluids system. During the detailed design and project planning phases, it was recognised that management of offshore logistics would be crucial, in particular the need to handle four different fluid types for each well. The rig's fluid handling capacity and solids-control equipment were significantly upgraded as a result and, in addition, the fluid provider commissioned a new fluids plant adjacent to the onshore operations base. Furthermore, the main supply boat was fitted with dedicated deck tanks to segregate brine and water-based fluid from the oil-based fluids. Contracting and Fluid Design Process A ‘pre-qualification’ was issued for the reservoir drilling and completion fluid services to protect the tight project deadline.