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A stimulation optimization study was recently conducted to design the acid recipes and execution programs for a new carbonate field in Abu Dhabi. The following paper outlines lessons learned and technical considerations that can improve the stimulation design of carbonate reservoirs. This particular field has a variety of extended horizontal completions ranging from open hole drains to liners with inflow control devices (ICDs). The following testing format can lead to immediate cost savings and long-term production increases in both green and brown fields. The Reservoir and Operation teams leveraged their expertise to place science firmly behind this important aspect of bringing a new field online. By being exact about the recipe testing procedure, the team made technical improvements to the existing recipes while also lowering the cost of stimulation.
The paper looks at the main issues associated with Integrity Management of aging export and loading systems (both topside equipment such as CALM buoys and subsea equipment such as pipelines and PLEMs) and discusses the main drivers forcing Operators to consider either replacing or upgrading their existing systems. Following a steep decline in oil prices at the end of 2014, which are likely to remain at present values for the near future, many Operators are looking at options to postpone planned procurement projects to replace aging equipment and are pursuing alternative strategies to maintain the output and uptime of their aging facilities. This paper discusses Integrity Management best practices, available to Operators to survey and maintain as well as manage the service life extension of their systems. The paper also addresses the options available when remediation works must be carried out. In particular, attention is focused on novel refurbishment activities which can be performed onsite whilst minimising the level of system downtime. Examples include: Refurbishment of CALM Buoys in drydock or on-site, relining of corroded subsea pipelines and removal/replacement subsea of damaged or corroded sections of pipeline. In conclusion, a number of cost comparison studies are presented to demonstrate the potential financial benefits of extending the remaining life of a system rather than replacing aging equipment with new.
As weight issues become increasingly apparent within the offshore construction industry, aluminium is gaining attention. By constructing large offshore platform/vessel parts from aluminium, the reduction in weight is significant: up to 60% less than steel. Replacing steel construction with full aluminium structures is not entirely feasible; thus the path forward lies in working with aluminium and steel together. Fabricating with aluminium requires a different approach starting with the earliest stages of the project. Only with innovative, out-of-the-box thinking can we use the attributes of aluminium to the fullest extent. Aluminium has valuable benefits; particularly in the harsh and highly corrosive seawater environment, for example, aluminium alloys used in the offshore industry corrode 100 times slower than steel, thus requiring little to no maintenance, resulting in a durable structure with a very low cost of ownership.
In general, an aluminium construction always outlives the platform. Despite all those great benefits, there are quite a number of preconceptions around using this material in construction projects; such as its behaviour in a fire, the complexity of welding, and its price. In this paper, we will address these assumptions and clear up popular misconceptions.
Zhang, Fuxiang (Tarim Oilfield Company) | Zhang, Hui (Tarim Oilfield Company) | Yuan, Fang (Tarim Oilfield Company) | Wang, Zhimin (Tarim Oilfield Company) | Chen, Sheng (Tarim Oilfield Company) | Li, Chao (Tarim Oilfield Company) | Han, Xingjie (Tarim Oilfield Company)
Keshen gas field, located in Kuqa Depression of Tarim Basin, northwest China, is an ultra-deep (7000m), high pressure and high temperature fractured tight sandstone gas reservoir with low permeability of 0.09mD and strong stress anisotropy about 30 MPa in horizontal stress contrast. For economic development, hydraulic fracturing is necessary in this reservoir.
To understand the mechanism of hydraulic fracturing and evaluate the fracability and fracture this reservoir efficiently, an integrated research has been conducted. We established a geomechanical model which described vertical and horizontal distribution of the geomechanical parameters in this reservoir. A fracturing experimental simulation was conducted with large size rock samples to analyze the interactive relationship between natural fractures and hydraulic fractures during fracturing. We also carried out a sensitive study to comfirm the key parameters for optimizing fracturing treatment design. Finally a new fracablity index calculation method suitable for fractured tight sandstone was built.
It is shown that for fractured tight sandstone reservoir with strong stress anisotropy like Keshen, shear deformation of natural fractures is a key factor of creating fracture area with high permeability. And the evolution of fracture area during fracturing experienced three processes. (1)Fracturing fluid extends along natural fracture at the initial fracturing stage; (2)At a certain injection pressure, slight shear deformation happens along the plane of natural fracture. As injection pressure increases, fracturing fluid breaks through a weak point of natural fracture and propagates along the direction of maximum horizontal stress; (3)A new set of fractures with combination of tensile-opening and shearing are formed, which are caused by changing of in-situ stress field around natural fractures. These three processes happen alternately and eventually form an ideal fracture area. It is also found that post-fracturing productivity has a close correlation with the shear deformation of natural fractures. At the axis of structure or fault developed area, natural fractures with strong potential shear deformation trend are more easily stimulated, and productivity can be high after fracturing. By contrast, fractures at structure saddle or steep part have weak potential shear deformation trend and are difficult to be stimulated, and thus productivity would likely be lower. Accoding to the mechanism of fracturing, we considered that the fracability of fractured tight sandstone is a function, and the parameters are in situ stress, shearing slip deformation, brittleness and fracture toughness.
Mechanisms of hydraulic fracturing and key factors effecting well productivity after fracturing in Keshen reservoir have been found through this study. Hydraulic fracturing treatment design and execution were conducted based on this study. After fracturing, the production performance (open flow potential) of stimulated wells increased by four-fold on average.
Cig, Koksal (Schlumberger) | Ayan, Cosan (Schlumberger) | Kristensen, Morten (Schlumberger) | Liang, Lin (Schlumberger) | El Battawy, Ahmed (Schlumberger) | Elshahawi, Hani (Shell) | Ramaswami, Shyam (Shell) | Mackay, Eric (Heriot-Watt University)
Relative permeability and capillary pressure curves are crucial inputs for a reservoir description. However, measuring these quantities on core samples in the laboratory is an extensive and time-consuming process. Wireline Formation Tester (WFT) logging is routinely applied in field operations for reservoir evaluation purposes. Often a historical record of WFT data exists for a field which can be re-interpreted, and since this interpretation takes days, rather than months to years in the case of core analysis, we propose in this paper to revisit the acquired WFT data with the purpose of estimating multiphase flow properties.
WFT logging is generally conducted in an open hole environment. By the time of logging, the near-wellbore region has been exposed to mud filtrate invasion. In the case of immiscible mud filtrate and formation fluid the invasion resembles a small scale water-flood process. During WFT sampling the mud filtrate is first cleaned and formation fluid subsequently sampled in a multiphase flow environment while measuring bottom-hole pressures and water-cuts. As shown in previous papers (
The proposed methodology starts with an open hole log interpretation which provides reservoir properties including a saturation distribution. The filtrate invasion is represented as accurate as possible from the open hole logs and drilling reports. WFT tool geometry and its internal tool storage and fluid segregation effects are incorporated into the modeling. A numerical forward model is then simulated within an optimization workflow where relative permeabilities, capillary pressures, damage skin, and depth of mud filtrate invasion are estimated by minimizing a misfit function between measured and modeled bottom-hole pressures and water-cuts. Industry accepted parameterization techniques are used for the relative permeability and capillary pressure curves. Initial parameter estimates are provided from the interpretations of the open hole logs, such as resistivity, dielectric, nuclear magnetic resonance, as well as from pressure transient analysis.
Previously we have studied WFT data from a 3D radial probe (3DRP) and a dual packer (DP) (
PETRONAS Carigali (PCSB) is the owner and operator of an extensive network of sub-sea pipelines which are situated offshore from main land Malaysia, in the South China Seas. Many of these pipelines run from platform to platform and platform to onshore facilities over distances of between several hundred meters to several kilometers and in varying depths of water. Severe internal corrosion, due in large part to Sulfate Reducing Bacteria (SRB) has caused some of the pipelines to have a drastically reduced life span which has historically resulted in the replacement of pipelines becoming necessary within a time period as short as four years. Historically, there has not been a viable methodology that could be utilized to install such a corrosion barrier within a sub-sea pipeline, thus the project for the design and development of InField Liner (IFL) system was instigated and within three years brought to a highly successful conclusion incorporating the full rehabilitation of an 8 pipeline carrying Crude media and which was due to been decommissioned within six months had the installation not gone ahead. This particular pipeline is now fully anticipated to provide a further 25 years of operational use to PCSB.
Borehole seismic surveys provide vital depth and velocity parameters needed to link surface seismic data with downhole log and well data. Furthermore they can deliver high-resolution subsurface images, detect anisotropy caused by natural fractures and help to monitor fluid movement depending on the chosen survey geometry. A borehole seismic survey, whether simple checkshots or a more complex VSP, is usually part of the initial data acquisition program in exploration and appraisal wells, but it is not uncommon that only the depth-time data from such a survey is used in seismic interpretation. This paper is intended for geoscientists working on subsurface projects to highlight information that can be gleaned from a VSP wavefield in addition to only a depth-time correlation.
This work presents a laboratory phase behavior study of Sodium Stearate/brine/oil system. The quantitative and qualitative observation of the phase behavior of the microemulsion in a three phase brine/oil/emulsion system is reported (Winsor III). The experiments were designed to investigate the stability, interfacial tension (IFT), and viscosity of the emulsion phase in a wide range of temperature (25-60 °C), water-to-oil ratio (0.2 to 5), salinity (10 to 200,000 ppm), and surfactant concentration. The range of parameters was selected as what typically occur during a chemical enhanced oil recovery (EOR) process. The effect of pH variations was also studied by changing that of the system from 1 to 11, using different acid and alkalines. As the pH increases, the stability of the emulsion phase increases as well as the emulsion phase thickness. The viscosity of the emulsion phase was also monitored qualitatively for different temperatures. Moreover, using longer chain alkanes confirms the capability of the surfactant for chemical EOR process.
Water flooding using seawater is a major oil filed operation implemented in different carbonate and sandstone reservoirs to maintain reservoir pressure and enhance oil recovery. However, due to the high sulfate content in the injected seawater, significant calcium, barium and strontium sulfate scale deposition can occur and cause severe formation damage. Typically, scale inhibitors are applied in the field to prevent the formation of calcium sulfate scale where they act either as chelating agents to form a soluble complex, as threshold inhibitors, which block the development of the supercritical nuclei or as retarders of the growth of the calcium sulfate crystals. The objective of this study is to evaluate the effectiveness of different types of scale inhibitors to prevent the formation of calcium sulfate scale during the injection of seawater into high-salinity bearing carbonate reservoirs.
Jar testing and SoftPitzerTM software were used to investigate the calcium sulfate precipitation due to the mixing of high calcium-content (37,000 mg/L) formation water and high sulfate-content (4,000 mg/L) seawater. This investigation was conducted on different mixtures of formation water and seawater at reservoir temperature of 155°F. Different types of scale inhibitors were tested to prevent the scaling of calcium sulfate in mixtures of seawater and formation water. The compatibility of these scale inhibitors with calcium ions present in formation water and also their effectiveness in preventing CaSO4 scaling were investigated using bottle testing. In addition, coreflood experiments were conducted to determine the adsorption behavior of these inhibitors in carbonate rocks.
Results showed that the application of two scale inhibitors (Acrylic homopolymer-based) can successfully mitigate calcium sulfate scale formation in seawater/formation water mixtures up to 155°F. Each one of these two scale inhibitors has its own effective minimum inhibition concentration (MIC). In addition to these results, the paper provides insights into the adsorption behavior of these inhibitors in carbonate rocks and how this affects their performance.
Noufal, Abdelwahab (Abu Dhabi company for Onshore Petroleum Operations Ltd (ADCO)) | Germay, Christophe (EPSLOG SA.) | Lhomme, Tanguy (EPSLOG SA.) | Hegazy, Gehad (Abu Dhabi company for Onshore Petroleum Operations Ltd (ADCO)) | Richard, Thomas (EPSLOG SA.)
This paper is focused on the integration of two laboratory centimeter-resolution logs of mechanical properties (strength and compressional elastic-wave velocity Vp) into an enhanced core analysis workflow for the geomechanical characterization of unconventional reservoirs in a giant field in Abu Dhabi, where fracking is the cornerstone for producing the unconventional oil. The design and placement of hydraulic fratures rely strongly on the
With this case study we illustrate: How the combination of the continuous profiles of rock strength UCS (Uniaxial compressive strength) and P-wave velocity measured directly on dry cores with the scratch tests contributes to the identification of different Geomechanical Facies, How the mapping of several Geomechanical Facies enables the building of a simple yet robust relationship between the UCS measured directly on cores and properties such as the total porosity and acoustic velocities of sonic waves, obtained from wireline logs, and How the centimeter-resolution profiles of strength and elastic wave velocities measured on dry cores enable the proper upscaling of geomechanical properties measured on plug samples to the entire cored section and the computation of a horizontal stress and brittleness profiles derived from unbiased geomechanical properties.
How the combination of the continuous profiles of rock strength UCS (Uniaxial compressive strength) and P-wave velocity measured directly on dry cores with the scratch tests contributes to the identification of different Geomechanical Facies,
How the mapping of several Geomechanical Facies enables the building of a simple yet robust relationship between the UCS measured directly on cores and properties such as the total porosity and acoustic velocities of sonic waves, obtained from wireline logs, and
How the centimeter-resolution profiles of strength and elastic wave velocities measured on dry cores enable the proper upscaling of geomechanical properties measured on plug samples to the entire cored section and the computation of a horizontal stress and brittleness profiles derived from unbiased geomechanical properties.
From this case study follows a general discussion on the relevance of wireline sonic logs relative to centimetric resolution data (scratch profiles or plug measurement) acquired on dry cores for the geomechanical characterization of reservoirs. We conclude that measurements on dry cores enable the more robust calibration of mechanical earth model and in turn better description of the reservoir mechanical response. The upscaled profiles of horizontal stress and brittleness index derived from dry core measurements would ultimately lead to an alternative strategy for the design and placement of hydraulic fractures along producing wells.