Tyrie, Jeb (Bridge Petroleum) | Mulcahy, Matt (Bridge Petroleum) | Leask, Robbie (Bridge Petroleum) | Wahid, Fazrie (Bridge Petroleum) | Arogundade, Olamide (Schlumberger) | Khattak, Iftikhar (Schlumberger) | Apena, Gani (Schlumberger) | Samy, Mohammed (Schlumberger) | Sagar, Rajiv (Schlumberger) | Xia, Tianxiang (TRACS International) | Nyadu, Kofi (WorleyParsons, Advision) | Maizeret, Pierre-David (Schlumberger)
This paper describes the proposed re-development of the Galapagos Field, comprising the abandoned NW Hutton field and the Darwin discovery (Block 211/27 UKCS) which forms a southerly extension. The paper covers the initial concept and analytical evaluation, the static uncertainty model build, the dynamic model history-match, the iterations between static and dynamic modelling, the development subsea and well locations, the optimisation workflow of the advanced Flow Control Valve (FCV) completions in both producers and injectors and the facilities constraints.
The redevelopment plan involved several multi-disciplinary teams. 20 years of production data from 52 wells were analysed to identify the production behaviour and confirm the significant target that provided the basis for the development concept selection. The full Brent sequence compartmentalised stochastic static model was based on reprocessed seismic plus 14 exploration and appraisal wells. Streamlines, uncertainty sensitivities and mostly good detective work honed a history match to RFT, BHP, PLT and oil and water production. P50, P90/P10 models were selected and over 100 FCVs optimised to deliver the profiles against an identified FSPO facilities’ constraints.
Over 1,000 static models were delivered consisting of sheet sands, incised valleys and channels in heterolithic facies overprinted by a depth trend with appropriate uncertainty ranges. The high well count gave a tight STOIIP probabilistic range of 790/883/937 million stb. The early RFTs illustrated extreme differential depletion between Brent zones and subzones of the Ness. To history-match these the dynamic model retained the static model definition in the Upper Ness to capture the thin but extensive shales. The early 18-month depletion and the late steady production-injection phases were simulated separately in prediction mode and matched the Production Analysis estimated ‘future’ production giving confidence to the history matched model. The initial concept development of 4 subsea-centres, to cover the large field area, with an injector in each compartment proved a robust selection. The horizontal wells increase PI where needed and mitigate internal faulting. The optimisation of the FCVs significantly increased oil production from all zones and drastically reduced water injection and production so that the identified FPSO modifications were relatively modest. The final First Stage Field Development Plan consists of 11 producers and 6 injectors across developed and undeveloped areas confirmed robust P50 reserves of 84 million boe.
Robust concept selection allowed for early identification of production units so that constraints and modifications could be accounted for within the economic model.
The Galapagos field re-development plan is an excellent example of how detailed static and fully history matched dynamic models can lay the foundations for new technology like the optimisation of the FCVs to access bypassed reserves using significantly smaller production units with reduced requirements for power, compression, gas lift, pumping pressure, injection and production. In short, they shrank the facilities.
Africa (Sub-Sahara) A drillstem test was performed on the Zafarani-2 well--located about 80 km offshore southern Tanzania. Two separate intervals were tested, and the well flowed at a maximum of 66 MMscf/D of gas. Statoil (65%) is the operator, on behalf of Tanzania Petroleum Development Corporation, with partner ExxonMobil Exploration and Production Tanzania (35%). The FA-1 well--located in 600 m of water in the Foum Assaka license area offshore Morocco--was spudded. The well targets Eagle prospect Lower Cretaceous resources. Target depth is 4000 m. Kosmos Energy (29.9%) is the operator, with partners BP (26.4%),
Africa (Sub-Sahara) Eni started production from the Nené Marine field, which sits in the Marine XII block in 28 m of water, 17 km offshore the Republic of the Congo. The first phase of the field produces from the Djeno pre-salt formation, 2.5 km below the ocean floor at a rate of 7,500 BOEPD. Future development will take place in several stages and will involve the installation of more production platforms and the drilling of at least 30 wells. Eni (65%) is the operator with partners New Age (25%), and Société Nationale des Pétroles du Congo (10%). The well's primary target is the Bunian structure: a four-way, fault-bounded anticline, which was defined by a 3D seismic survey. It will be drilled to a total depth of 1682 m.
The negative impacts of high water cut in mature fields are well known within the oil & gas industry. Water production preventive & mitigative measures are well established and documented: Wireline or coil tubing conveyed diagnostic and work-over operation(s) is one of such common preventive measures. This paper, through a series of integrated case studies will highlight the best practices for wireline conveyed logging and work-overs with one common goal, i.e. to achieve the water production to a minimum acceptable level in deviated high water cut wells.
The prolific XYZ field is located in the Northern North Sea and it produces oil from Jurassic Brent Group. Oil production from the XYZ reservoir started in early 1978, with 43 producing wells and 15 water injection wells targeting the Rannoch, Etive, Ness and Tarbert sands. Oil and gas production peaked in 1982 and since then production has steadily declined for this field. The increasing water cut in the wells of this field is presenting a challenge for the operating companies.
Production profiling using advanced Production Logging data, casing/tubing integrity check using Multi-Finger Caliper data and saturation monitoring using cased-hole Reservoir Saturation data was done in these wells to ascertain the water producing zones and do the subsequent well intervention, if required. A strategic diagnostic test was designed to precisely evaluate the flow profile using advance production logging tool consisting of 5 mini-spinners & 6 sets of each electrical and optical probes; Real-time data assessment and analysis was done for different flowing rate surveys to validate the findings. Additionally, casing condition was evaluated using Multi-Finger Caliper to decide Plug or Straddle setting depths. Also, new hydrocarbon bearing zones were identified based on cased-hole saturation tool results. The analysis results boosted the cumulative oil production.
This study demonstrates the importance of making real time interpretation decisions at the wellsite and the benefit of developing a good working relationship between wellsite engineers and onshore technical support. The results of this work led to the unequivocal determination of major oil and water producing zones in deviated high water cut (95%+) wellbores which further helped in taking workover decisions to carry out water shut off, utilizing either plug or straddle technology. The findings of caliper data determined the appropriate plug or straddle setting depths. The results were compared and confirmed with the nearby well dynamic pressures and production data.
The technical approach and processes applied to wells of XYZ field is a valuable example guide to decide water shut off zones and technique of similar plays. This study consists of three integrated case studies from a mature field where water shut-off zones and technologies were decided based on the findings of production logging and well integrity data. Also, re-perforation jobs were performed based on the cased-hole reservoir saturation data results. These strategic workover operations ultimately led to significant increase in hydrocarbon production.
The performance of many improved and enhanced-oil-recovery (EOR) techniques in conventional reservoirs is frequently degraded by conformance problems. The presence of high-permeability streaks or thief layers between injection and production wells typically results in premature water breakthrough, high water cut, and deficient volumetric sweep. As a result, significant oil volumes in the reservoir might not be contacted by the injection fluid.
Several conformance-improvement techniques (e.g., foams, gels, resins) have been developed and practiced in improved-oilrecovery operations. Each technique has its own advantages and limitations related to deployment practicality, effectiveness, and durability. In this paper, we introduce a novel conformance-improvement method (CIM) that we consider practical, effective, and durable. The CIM process consists of cyclical injections of pulse slugs of surfactant alternating with brine. The slug compositions are selected on the basis of the rheological behavior of the microemulsion phase. The chemical slugs are configured such that the viscosity of the injected fluids is kept low to preserve injectivity and to ensure the invasion of the conformance agent toward the thief zones. The trailing brine slugs are designed to produce a high-viscosity microemulsion as they mix with the leading surfactant slugs in the reservoir. The proposed process leads to a reduction in the effective mobility of the fluids in the thief layers. As a result, the chase waterflood (WF) would divert into previously uncontacted layers to improve the sweep efficiency.
The potential of the proposed CIM in improving oil recovery is demonstrated by various simulations of reservoir cases under waterflooding. We performed various sensitivities to investigate the effectiveness of the proposed process that include well spacing, permeability contrast, size of the thief layers, heterogeneity, and the size of the chemical pulse slugs. Simulations showed that this process is effective in addressing reservoir-conformance issues, and therefore it has the potential to improve the sweep efficiency and the recovery factor (RF) in reservoirs with distinct thief layers. The treatment surfactant volumes are relatively small, which enables this process to be cost-effective.
Water-alternating-gas (WAG) injection is a technique employed in EOR (Enhanced Oil recovery). WAG injection can be immiscible or immiscible with water and gas being injected into the hydrocarbon liquids reservoir to promote greater recovery. WAG injection is effective as gas typically has greater microscopic sweep efficiency whilst water has better macroscopic sweep efficiency. It is important to be able to characterise and quantify how much the degree and type of small/medium scale heterogeneity during WAG flooding could affect the recovery factor from a reservoir, such that during project evaluation teams are able to properly evaluate the ranges on uncertainty on recovery factors and the economic benefit of the project as well as risks associated with WAG implementation.
The Hutton field is located in the North Viking Graben area of the North Sea and the lithology of the reservoir section is made up of Brent group sandstones which are highly heterogeneous in the horizontal and vertical directions at a small scale (i.e. pore scale and plug scale) and at a medium scale (the vertical layering of different formations).
The effect of reservoir heterogeneity on WAG efficiency has been evaluated using dynamic reservoir simulation models of the Hutton field. Input parameters were based on an available model of the Hutton Field. A fine grid geological model (grid size 5ft × 5ft × ~2ft) has been created of a small section of the Hutton reservoir. A variety of field development schemes were evaluated including depletion, water injection, gas injection and immiscible WAG production scenarios. Geological models were created for three scales of heterogeneity (small scale and medium scale heterogeneity models, and a homogeneous model) based on interpretation of log data from a set of three control wells. Compositional simulation models were used to model the dynamic behaviour. Two phase relative permeability (oil / water and gas / oil) data was used, as three phase relative permeability data for Hutton was not available. There is no hysteresis data available for the Hutton field, therefore separate test runs were carried out to evaluate how hysteresis might affect recovery factor during WAG injection using two and three phase relative permeability data and parameters for use in the Killough correlation for hysteresis.
Immiscible WAG injection is beneficial in reservoirs with small and medium scale heterogeneity and gives ~5% improvement in recovery factor when compared to water injection. However, when hysteresis is included, the recovery factor may be higher than this by another ~10%. WAG injection may provide inferior recovery factors to water injection in homogeneous reservoirs. However, simulations indicated that some limited gas injection into a homogeneous reservoir may prove beneficial for accessing attic oil. It is recommended that laboratory testing of core samples (core flood experiments) be carried out prior to a WAG injection specifically with the aim of identifying the most appropriate hysteresis model and to give good relative permeability data across all three phases.
The performance of many improved and enhanced oil recovery techniques in conventional reservoirs is frequently degraded by conformance problems. The presence of high permeability streaks or thief layers between injection and production wells typically results in pre-mature water breakthrough, high water cut and deficient volumetric sweep. As a result, significant oil volumes in the reservoir may not be contacted by the injection fluid.
Several conformance improvement techniques (e.g. foams, gels, resins) have been developed and practiced in improved oil recovery operations. Each technique has its own advantages and limitations related to deployment practicality, effectiveness, and durability. In this paper, we introduce a novel conformance improvement method (CIM) that we consider to be practical, effective and durable. The CIM process consists of cyclical injections of pulse slugs of surfactant alternating with brine. The surfactant slug compositions are selected based on the rheological behavior of the microemulsion phase. The chemical slugs are configured such that the viscosity of the injected fluids is kept low to preserve injectivity and to ensure invasion of the conformance agent towards the thief zones. The trailing brine slugs are designed to produce a high-viscosity microemulsion as they mix with the leading surfactant slugs in the reservoir. The proposed process leads to a reduction in the effective mobility of the fluids in the thief layers. As a result, the chase waterflood would divert into previously uncontacted layers to improve sweep efficiency.
The potential of the proposed CIM in improving oil recovery is demonstrated by various simulations of reservoir cases under waterflooding. We performed various sensitivities to investigate the effectiveness of the proposed process that include well-spacing, permeability contrast, size of the thief layers, heterogeneity, and size of the chemical pulse slugs. Simulations showed that this process is effective in addressing reservoir conformance issues, and therefore it has the potential to improve sweep efficiency and recovery factor in reservoir with distinct thief layers. The treatment surfactant volumes are relatively small, which enables this process to be cost-effective.
Oil recovery from a subsurface reservoir is typically expressed as the product of displacement and sweep efficiencies (Lake et al., 2014). The first is defined as the ratio of displaced to contacted volumes, while the second is defined as the ratio of contacted to in place volumes. Reservoir conformance is a measure of the volumetric sweep efficiency during oil recovery processes (Sydansk and Romero-Zeron, 2010). Conformance problems can be caused by the presence of high-permeability streaks, thief-layers, faults, or fractures in the reservoir. These geological features act as preferable conduits for the injected fluids, therefore causing significant oil zones in the reservoir to be unflooded. One of the key gaps in poorly managed IOR/EOR projects is the lack of diagnosis and treatment of the conformance problems (Sydansk and Romero-Zeron, 2010). Conformance improvement methods should be low-risk and low-cost procedures within the reservoir management workflow that result in a quantifiable increase in oil recovery.
The existing literature provides little guidance on the relevance of formation damage or return permeability results obtained from reservoir-conditions core flood testing on sandstone cores with heavy formate fluids. The drilling and completion in open hole of all six production wells in the Huldra field with heavy formate fluid provided a rare opportunity to appraise the results from HPHT core flood testing carried out on Ness (North Sea Brent Group) sandstone reservoir cores as part of the original drilling fluid qualification process for the Huldra development program.
Low- and high-permeability sandstone core plugs obtained from the productive Ness reservoir formation in the Huldra field were subjected to static and dynamic exposure to heavy formate drill-in fluids under HPHT reservoir conditions at 350 psi overbalance for a period of 296 hours. The cores were then exposed to short-duration drawdowns under HPHT reservoir conditions to simulate the very early phase of production start-up. The permeability impairment results obtained in these laboratory tests were compared against the production performance data for six Huldra field wells drilled and completed with sand screens in open hole in Brent Group sandstones with the same heavy formate fluids.
The reservoir-conditions (11,400 psi, 150°C) core flooding test with a SG 1.92 formate drill-in fluid sample from a Huldra well drilling job reduced the permeability of a 1416 mD Ness core by 37.8%. The same fluid reduced the permeability of a 2.8 mD Ness core by 65.9%. Repeating the same reservoir-conditions core flooding tests with a fresh SG 1.92 formate drill-in fluid sample prepared in the laboratory gave very similar results. In all cases the permeability of the cores was restored to original levels by soaking the wellbore face of the cores at balance for 24 hours with 15% acetic acid under reservoir conditions. The full restoration of permeability by non-invasive soaking of the core faces with dilute organic acid at balance suggested that the source of the tractable impairment was residual CaCO3/polymer filter cake still pressed onto the core face after lengthy drilling fluid exposure at overbalance and a very short clean up by drawdown.
The six Huldra production wells were drilled with SG 1.92 formate fluid at 37°-54° inclinations through the Tarbert, Ness, Etive and Rannoch reservoir formations and completed in open hole with 300-micron single-wire-wrapped screens. The wells cleaned up naturally during production start-up, without the need for acid treatment, resulting in skins that were at the low end of the expected range. The Hudra field was shut down in 2014 after producing 17.3 GSm3 of gas, representing an 80% recovery of the original gas in place.
This has been a useful first appraisal of a set of historical return permeability test results obtained with heavy K/Cs formate fluids. As more data become available from other HPHT gas condensate fields developed entirely with heavy formate brines (e.g. the Kvitebjørn and Martin Linge fields) it may become possible to assign some predictive value to the results of return permeability tests with these fluids.
Casing and liner drilling is widely regarded as a method to overcome challenges related to formation instability. Its use and experience is gradually gaining foothold as its benefits and functionality in many cases can be the solution and risk mitigation to overcome some of the Oil & Gas industry's challenges related to drilling wells with narrow drilling margins, depletion and formation instability challenges in traditional well construction. The technology has now been matured over the last 5 years and, even though the full potential has yet to be fully explored, several "un-drillable" wells have been made drillable by using its ability to combine the drilling and logging in complex 3D wells while simultaneously securing the wellbore. The second generation of the technology is currently being field trailed as 7in system, but several different configurations are already available, including a 6 8 ¾″ Integrated Underreamer, inner BHA repositioning functionality to remove 6″ rathole for the BHA along with several simple but very robust solutions for liner reaming purposes. The traditional Steerable Drilling Liner System (SDL) is available for 8 ½ and 12 ¼″ holes sizes, whereas the second generation will initially be available for 8 ½ - 8 ¾″ hole sizes. This paper will focus on benefits and experiences from using the technology along with an update on the new features that is gradually being made available as part of the second generation SDL technology.
Multiscale methods have been developed as a robust alternative to upscaling and to accelerate reservoir simulation. In their basic setup, multiscale methods use both a restriction operator to construct a reduced system of flow equations that can be solved on a coarser grid and a prolongation operator to map pressure unknowns from the coarse grid back to the original simulation grid. When combined with a local smoother, this gives an iterative solver that can efficiently compute approximate pressures to within a prescribed accuracy and still provide mass-conservative fluxes. We present an adaptive and flexible framework for combining multiple sets of such multiscale approximations. Each multiscale approximation can target a certain scale; geological features such as faults, fractures, facies, or other geobodies; or a particular computational challenge such as propagating displacement and chemical fronts, wells being turned on or off, and others. Multiscale methods that fit the framework are characterized by three features. First, the prolongation and restriction operators are constructed by use of a nonoverlapping partition of the fine grid. Second, the prolongation operator is composed of a set of basis functions, each of which has compact support within a support region that contains a coarse gridblock. Finally, the basis functions form a partition of unity. These assumptions are quite general and encompass almost all existing multiscale (finite-volume) methods that rely on localized basis functions. The novelty of our framework is that it enables multiple pairs of prolongation and restriction operators—computed on different coarse grids and possibly also by different basis-function formulations—to be combined into one iterative procedure.
Through a series of numerical examples consisting of both idealized geology and flow physics as well as a geological model of a real asset, we demonstrate that the new iterative framework increases the accuracy and efficiency of the multiscale technology by improving the rate at which one converges the fine-scale residuals toward machine precision. In particular, we demonstrate how it is possible to combine multiscale prolongation operators that have different spatial resolution and that each individual operator can be designed to target, among others, challenging grids, including faults, pinchouts, and inactive cells; high-contrast fluvial sands; fractured carbonate reservoirs; and complex wells.