Offshore Reservoirs Research Articles

Remaining Oil Distribution and Development Strategy for Offshore Unconsolidated Sandstone Reservoir at Ultrahigh Water-Cut Stage

Due to the influence of long-term waterflooding, the reservoir physical properties and percolation characteristics tend to change greatly in offshore unconsolidated sandstone reservoirs at ultrahigh water-cut stage, which can affect the remaining oil distribution. Remaining oil characterization and proper development strategy-making are of vital importance to achieve high-efficiency development of mature reservoirs. The present numerical simulation method is difficult to apply in reservoir development due to the problems of noncontinuous characterization and low computational efficiency. Based on the extended function of commercial numerical simulator, the time-varying equivalent numerical simulation method of reservoir physical properties was established, and the research of numerical simulation of X offshore oilfield with 350,000 effective grids was completed. The results show that the time-varying reservoir properties have a significant impact on the distribution of remaining oil in ultrahigh water-cut reservoir. Compared with the conventional numerical simulation, the remaining oil at the top of main thick reservoir in X oilfield has increased by 18.5% and the remaining oil in the low-permeability zone at the edge of the nonmain reservoir has increased by 27.3%. The data of coring well and the implementation effect of measures in the X oilfield are consistent with the recognition of numerical simulation, which proves the rationality of numerical simulation results. The new method is based on a mature commercial numerical simulator, which is easy to operate and has reliable results.

Experimental investigation of carbon dioxide flooding in heavy oil reservoirs for enhanced oil recovery

With the attention paid to greenhouse gas emission reduction all over the world, CO2 capture, utilization and storage technology has developed rapidly. Predecessors have done a lot of work on the effect of CO2 on properties of the oil, the changes of parameters after CO2 injection are different. Through PVT, slim tube test and phase state simulation, this work studied the influence law of CO2 injection on the properties of heavy oil in offshore reservoirs in eastern China. It defines the adaptability and oil displacement mechanism of CO2 flooding in the reservoirs. In this work, 12 oil displacement experiments were carried out to quantify the effect of injection sequence, slug size, gas injection rate, and soaking time on oil recovery in the hydrogen carbon reservoir. These experimental results have indicated the influence of different factors on oil displacement effect. It provides strong evidence for the efficient development and enhanced oil recovery of the oilfield. The results indicate that the gas–water alternative injection is better than continuous water flooding or continuous CO2 flooding by improving the ultimate recovery at 8.9% and 12.7% respectively. A larger CO2 slug is beneficial to improve the ultimate oil recovery and the injection rate of CO2 slightly affects the ultimate oil recovery factor. Longer soaking time can improve the ultimate recovery either. The ultimate recovery increases rapidly with the soaking time when it less than 24 h, but the ultimate oil recovery hardly increases when the soaking time is longer than 24 h.

An integrated remote sensing and biomarker maturity parameter-based approach to trace petroleum migration in a complex fault zone lineament of the Brazilian Equatorial Margin

The present paper investigates the oil migration and lineament distribution in fault zones within a sedimentary basin, showcasing the results from an integrated use of geochemical, and remote sensing data along the Fazenda Belém Fault Zone (FBFZ) in the Potiguar Basin, Brazilian Equatorial Margin. Lineaments were detected from a LiDAR digital elevation model data set using the quantitative method of morphology recognition based on horizontal and vertical curvature calculation and mapping. The polynomial regression-based spatial distribution of 20S/(20S + 20R) C29 steranes is successfully used in oils from offshore and onshore reservoirs of the Potiguar Basin, tracing field-scale oil migration direction. These multidisciplinary analyses revealed that the oil initially migrated from an offshore area along the NE-oriented fault zone, and then parts moved along the branches of this zone to finally reach the areas of the onshore reservoirs. In addition, NE-oriented lineaments enhanced the near-surface fluid circulation, while they commonly correspond to the topographic features and fault zones. Anisotropy tensors and slip- and dilation tendency calculated from the lineament map also indicate that the geometric complexity of the lineament pattern is influenced by present-day and partitioned stress fields in the Potiguar Basin. The integration of remote-sensing and geochemistry analyses at the FBFZ area proved to be effective in approaching the tectonic aspects of a fault zone in a petroleum basin, as well as in investigating the field-scale migration of oil along the fracture corridor in a fault zone.

Data-driven offshore CO2 saline storage assessment methodology

The world produces approximately 50 billion tonnes of greenhouse gases annually. This is measured in CO2-equivalents, and geologic CO2 storage has the potential to advance decarbonization and mitigate greenhouse gas emissions. New technologies to assess offshore carbon storage are needed to address resource, regulatory, and commercial needs. Although most efforts to assess storage resources focus on onshore criteria, offshore reservoirs offer significant storage potential and distinct development challenges. Potential advantages of offshore carbon storage include being further from human population centers and less potential to interact with groundwater. The U.S. Department of Energy's method for evaluating storage capacity in non-oil-bearing saline reservoirs has been enhanced to support assessments for offshore environments in the Offshore CO2 Saline Storage methodology (OCSS). This methodology applies data-driven capabilities to estimate saline storage capacity while accounting for features specific to offshore reservoirs. Features include changes in CO2 density and sedimentary differences that impact estimates of permanence and capacity. The Offshore CO2 Saline Storage Calculator mechanizes OCSS to estimate storage capacity. This paper presents the methodology and estimates for 18 geologic domains in the Gulf of Mexico. Potential storage distributions, sensitivity analyses, and the incorporation of spatial data and tools to support safe site selection are also discussed.

Impact of model and data resolutions in 4D seismic data assimilation applied to an offshore reservoir in Brazil

Data assimilation is the process where reservoir models are calibrated using dynamic data. The goal is to reduce uncertainties related to reservoir properties for more assertive model-based forecasts and decisions. The use of 4D seismic data as input to this process allows model properties to be updated so that dynamic changes are better represented in the entirety of the reservoir. However, in many cases, the higher the number of grid blocks, the more time consuming are the models' simulation. Thus, the balance between the fidelity of models and simulation runtime in a project is crucial in the planning of activities. The objective of this work is to discuss the impact of using grids with different resolutions and explore options to incorporate 4D seismic maps in data assimilation and production forecast. Through a real field application, we evaluate the use of two grids with different vertical and lateral resolutions, using the Ensemble Smoother with Multiple Data Assimilation (ES-MDA) method. The available high-quality seismic data, applied to a Bayesian inversion, generated 4D impedances that helped identify important dynamic changes that happen at intermediate layers of a thin reservoir (averaged 25 m thickness), located in Brazil. Thus, we also evaluate two approaches for models updating with 4D seismic data: treating the entire reservoir as a single interval, and considering a greater vertical resolution by adding information at intermediate layers. Overall, well production misfits between posterior models and observed data were considerably reduced when assimilating seismic and production data simultaneously, presenting even smaller errors than production data only cases. This happened for both grids. By adding further 4D information at intermediate layers with the use of two maps, we observed (in both grids) that posterior models could predict important reservoir behaviors, such as the gas trapping in the deeper interval. The coarser grid presented lower well production data misfits compared to the refined grid, but showed to be insensitive to the use of different seismic data in data assimilation, resulting in alike models. Furthermore, the posterior models for the coarse grid presented similar behaviors when performing production forecast, which indicates that the uncertainties may be underestimated in these cases. The refined grid presented slightly greater production misfits but was more sensitive to the different 4D seismic inputs. In this grid, an increased ensemble variance was observed between the posterior models, which is also observed in the long-term forecasts. Also, the most refined grid yielded estimates of acoustic impedance changes visually closer to the observed data than those obtained from the coarser grid. As a real case application, the definition of the best procedure is not straightforward. Results suggest that both grids can be used depending on the project's objective. The coarser grid is a good option for short-term studies, since it is able to properly represent the near future with much cheaper models. The refined grid may be suitable for long-term decisions, because it better represents models' uncertainties and provides safer risk analyses.

Case Study: Space-Age Directional Drilling Improves Efficiency, Economics

Directional drilling has been used in oil and gas operations since the 1930s when onshore drillers employed the technology to reach offshore reservoirs. Over the years, technologies have been introduced to improve precision and control and at the same time have allowed multiple reservoirs to be produced through a single well, which reduces drilling costs and minimizes the environmental impact of the drilling process. In designing drilling plans, operators have considered economics when deciding whether to employ the traditional process of rotating the drillstring to control well trajectory or use more precise directional drilling techniques, but an either/or approach is not always the best one. The introduction of software that analyzes drilling conditions and determines the most appropriate drilling solution is changing the status quo, streamlining the drilling process and changing the playing field for drillers. The Evolution of Directional Drilling The widespread adoption of horizontal drilling from narrowly spaced slots on a centralized pad location has led to the introduction of complex wellbore geometry intended to maximize field development while minimizing geographical footprint. The growing need for precise execution of complicated well trajectories increased the demand for directional drilling expertise. Using a steerable bottomhole assembly (BHA) comprising a mud motor with a bent housing, an experienced directional driller can orient the bend of the motor in the direction prescribed on the well plan to steer the well on the intended trajectory in a process known as sliding. When the well trajectory is intended to remain relatively straight, the entire drillstring is rotated from surface in a process referred to as rotating. Experience and research have shown, however, that the well trajectory is rarely straight during periods of rotation due to rotational tendencies, a combination of systematic and random influences from BHA design, drilling parameters, and geological formation characteristics that can cause a significant divergence from plan. Rotational tendencies, along with designed well plan deviations, often require sliding to ensure the well follows the planned trajectory. All else being equal, it might seem that sliding should be applied across the board, but there are two reasons that sliding is not the default solution.

Production Analysis of Horizontal Wells in a Two-Region Composite Reservoir Considering Formation Damage

The horizontal well is extensively used to exploit oil at the Bohai offshore oilfield, China. It has been proved by practice that formation damage always happens during the production of wells. However, it is a challenging task to evaluate the formation damage for horizontal wells. In this paper, a flow model considering formation damage is established for horizontal wells. The reservoir geometry is divided into two regions: the inner region represents the region of formation damage and the outer region that without damage. The finite element method is used to solve the flow model. The well production rate can be determined by using the material balance method. For different scenarios, such as when the horizontal well is completely in the inner region or when the horizontal well passes through two regions, the effects of some key parameters such as damage radius, damage region permeability, and well position on the oil production rate and pressure distribution characteristics are analyzed. The results show that a smaller damage radius, higher damage zone permeability, and a horizontal well closer to or in greater contact with the outer region result in a higher oil production rate and faster pressure drop propagation. The presented model and obtained results enrich production analysis of horizontal wells in a two-region composite reservoir considering formation damage, which has significance for efficient offshore reservoir development.

Failure Mechanism Analysis of Bonded Joint with Fiber Reinforce Plastic (FRP) Sucker Rod in Offshore Reservoirs

At present, fiber reinforce plastic (FRP) sucker rod has the advantages of high tensile strength, light weight and strong corrosion resistance which gradually applied and popularized in offshore oil and gas field. However, the bonded joint of FRP sucker rod is particularly prone to break and fall off. Current research works mainly focus on the mechanical properties of FRP sucker rod and less consideration was given to adhesive performance. This paper proposed a finite element model (FEM) of bonded joint. The maximum predicted load of bonded joint was acquired and the axial distribution of adhesion stress and slip distance in the bonding interface was studied, which can provide theoretical basic of bonded joint and extend the service life of downhole pumping operation.

Consistency and prior falsification of training data in seismic deep learning: Application to offshore deltaic reservoir characterization

Deep learning (DL) applications of seismic reservoir characterization often require the generation of synthetic data to augment available sparse labeled data. An approach for generating synthetic training data consists of specifying probability distributions modeling prior geologic uncertainty on reservoir properties and forward modeling the seismic data. A prior falsification approach is critical to establish the consistency of the synthetic training data distribution with real seismic data. With the help of a real case study of facies classification with convolutional neural networks (CNNs) from an offshore deltaic reservoir, we have highlighted several practical nuances associated with training DL models on synthetic seismic data. We highlight the issue of overfitting of CNNs to the synthetic training data distribution and propose regularization strategies to address it. We demonstrate the efficacy of our proposed strategies by training the CNN on synthetic data and making robust predictions with real 3D partial stack seismic data.

Evaluation of distinct soft-sediment deformation triggers in mixed carbonate-siliciclastic systems: Lessons from the Brazilian Pre-Salt analogue Crato Formation (Araripe Basin, NE Brazil)

Soft-sediment deformation structures (SSDSs) are ubiquitous in several depositional sedimentary environments and can be triggered by autogenic- and allogenic-related mechanisms. SSDSs identification in the geological record is more frequent in siliciclastic deposits, from which the most accepted models were developed. Given the fact that carbonate rocks have rapid diagenesis, which results in changes in the rheological behavior of deformational processes in short time, these are excellent facies for exploring past deformational mechanisms in a given sedimentary basin. Here, we describe distinct SSDSs developed in mixed carbonate-siliciclastic successions deposited in an Early Cretaceous lacustrine depositional system (carbonate-dominated) subjected to recurrent epicontinental marine ingressions (siliciclastic-dominated). Deformation occur in some siliciclastic intervals but it is more common in carbonate beds. Facies associations analysis combined with detailed outcrop description of the SSDSs allowed the recognition of seismic- and non-seismic-generated structures. Two km-scale, laterally continuous carbonate beds, characterized by deformation-bearing horizons, are interpreted to be the result of seismic shocks. Conversely, most of the recognized SSDSs cannot be confidentially interpreted as seismites. Autogenic triggers and criteria for accessing the origin of deformation mechanisms in both carbonate- and siliciclastic-dominated settings are alternatively proposed. Assessing such criteria is fundamental for differentiatte the timing and range of deformation and are here discussed in the context of the offshore petroleum reservoirs in the Brazilian Pre-Salt successions, where lacustrine carbonates were probably subjected to a similiar superposition of syn-sedimentary seismicity and later events of salt-tectonics and hydrotermalism.

Numerical investigation and structural optimization of bonded joints with fiber reinforce plastic sucker rods in offshore reservoirs

ABSTRACT Sucker rod constructed of FRP (fiber-reinforced plastic) is currently used in offshore oil and gas industries due to its high tensile strength, lightweight, and resistance to corrosion. Due to the fact that the surface of FRP sucker rod cannot be threaded, it is often attached to steel joints via adhesive technology, and the bonded joint of FRP sucker rod is particularly prone to breaking and coming off. The current research is primarily concerned with the mechanical properties of FRP sucker rods, with little emphasis on the adhesive performance of bonded connections. This research developed a numerical model with a novel bonded joint structure based on the cohesion failure criteria. An indoor test was used to determine and confirm the expected bonded joint failure load. Additionally, an orthogonal test was conducted to maximize the adhesion performance. The findings indicated that a) theaccuracy of numerical model was within 2% and b) when the groove angle was 30°, the length ratio was 2/23, each groove was 14 mm in length based on a triangular groove, and the anticipated failure stress of the bonded joint was around 443 kN, an increase of 10%.

Perturbative-Integro-Differential Solution for the Nonlinear Hydraulic Diffusivity Equation for Infinite-Acting-Oil Flow in a Permeability-Pressure-Sensitive Reservoir

Summary The nonlinear hydraulic diffusivity equation (NHDE) models the isothermal single-phase Darcian flow through porous media considering the variation in the properties of the rock and the fluid present inside its pores. Typically, the dimensionless solution of the linear hydraulic diffusivity equation (LHDE) pD⁢(rD,tD) for constant permeability oil flow in porous media is computed through Laplace and Fourier transform or Boltzmann transformation. For these cases, the dimensionless general solution in cylindrical coordinates is expressed by the transcendental function exponential integral Ei(rD,tD). This work develops analytically a new coupled perturbative-integro-differential model to solve the NHDE for oil flow in a permeability-pressure-sensitive reservoir with source. The general solution is computed combining a first-order asymptotic series expansion, Green’s functions (GF), and a Volterra’s second kind integro-differential formulation. A set of pore pressure and permeability values for two sandstones samples in an offshore reservoir from Brazil is obtained experimentally using the geomechanical elastic parameters (e.g., the Young’s modulus and Poisson’s ratio in addition to a uniaxial cell). These data are used as input in the computational code to run the analytical model and evaluate the reservoir permeability change. After these data input, the model runs and it allows to compute the instantaneous reservoir permeability values over the well-reservoir life cycle. The model calibration is performed by comparing the developed solution with a numerical porous media oil flow simulator named IMEX®, widely used in reservoir engineering and well-testing field operations and scientific works. The general solution of the NHDE mD(rD,tD) is computed by the sum of the linear solution pD(rD,tD) (constant permeability) and the first-order term of the asymptotic series expansion mD(1)(rD,tD), composed of the nonlinearity present in solution caused by the reservoir permeability variation. The results have shown that the developed solution is accurate, when compared to the numerical simulator, providing to be an attractive mathematical tool to help the well-reservoir management due to its low computational costs, when compared to the numerical simulators acquisition costs.

Experiment and Simulation of One Deep Sewage Discharge Type: Transport of Low‐Salinity Sediment‐Laden Flow Discharged

AbstractDeep sewage discharge leads to inestimable damage to the ambient water (lakes, oceans and reservoirs), which has caused widespread social concern. In the current paper, a three‐dimensional (3D) buoyancy plume model for deep sewage discharge was developed. It simulates sediment‐laden flow with the effects of temperature and salinity differences. Taking the turbulent diffusion coefficient of salinity (αsal) as the calibration parameter, a comparison between the RNG k‐ε and the standard k‐ε models was performed. The proposed model was verified well and agreement with experiment, which proved that the RNG model with the αsal value of 0.4 was the optimal calibration. Then the model was applied to quantify the behavior of the buoyant plume in the ambient fluid (salt water) with respect to different contours of turbulent kinetic energy (k), temperature, salinity and sediment. The dimensionless centerline trajectory positions and boundary positions of them were determined. The results indicated that the discharge of low‐salinity sediment‐bearing water influenced the deep ambient water spatially, both near the free surface and in the vertical plane. Different diffusion and spreading shapes (butterfly, Ginkgo biloba, bean) can be observed on the surface. Accurately evaluating the impact of deep discharge on ambient water has great significance for maintaining healthy and sustainable environments in offshore areas, deep lakes and reservoirs.

Carbon capture and storage in the coastal region of China between Shanghai and Hainan

In this study, we evaluate offshore carbon capture and storage (CCS) opportunities in the coastal region of China between Shanghai and Hainan. A plant-by-plant analysis of stationary CO2 emission and field-by-field evaluation of CO2 sinks are presented. Results show that CO2 emission from power plants is 1.0 Gtpa while that from refineries, iron and steel mills, and cement factories is 0.7 Gtpa. The available locations to store CO2 are offshore oil and gas reservoirs and saline aquifers in the East China Sea and the West Taiwan, Pearl River Mouth, Yinggehai, Qiongdongnan and Beibuwan basins. There is 624 Gt of mid CO2 storage capacity and 432 MMbbl of CO2-enhanced oil recovery (EOR) or enhanced gas recovery (EGR) potential in these basins, which is enough to store 367 years of stationary CO2 emission. Of this, 623 Gt come from saline aquifers, 1.5 Gt from gas reservoirs, and only 0.3 Gt from oil reservoirs. A CO2 source-sink mapping exercise reveals that almost all stationary CO2 sources in the coastal region of China can be stored in offshore CO2 sinks within a 350 km distance and many within a 200 km distance. Candidates for first mover offshore CCS projects include the Huizhou, Xijiang, Wenchang, Panyu and Enping oil fields.

Case Study: Smart Liner Matrix-Acid Stimulation—A Cost-Effective Performance-Enhancement Technique for Carbonate Reservoirs

Carbonate reservoirs require effective acid stimulation to improve well productivity. For long horizontal wells, a complicating factor has previously been the difficulty of controlling acid placement along the reservoir section. The Smart Liner (SL) concept solves this problem. It consists of a number of small holes spaced in such a way so as to distribute acid evenly along the reservoir interval. Fig. 1 shows a schematic of the concept. Without the need of a coiled tubing, acid is bull-headed at a high rate from surface through the production tubing and enters the liner from the left. The liner does not have to be horizontal but very often is. When acid reaches the first hole, which typically has a diameter of 3–6 mm, the pressure drop across the hole is so large that only a small portion of the acid exits the liner through the hole; the remaining acid continues along the liner until it reaches the next hole where the process is repeated. Appropriate hole spacing ensures that acid is distributed with a given acid coverage (dosage) in barrels of acid per foot of reservoir section. The small cross-sectional area of the holes results in focused acid jetting at velocities often exceeding 20 m/s (65 ft/s). The jetting helps promote wormhole formation leading to substantial productivity enhancement. The hole-spacing design requires dedicated software which must take into consideration constraints pertaining to the reservoir, the well, and the pumping equipment while minimizing operational complexity. The tool should also yield a quick answer to enable the user to optimize the final design post drilling and provide a running tally consisting of the sequence of liner joints to be run in hole. In heterogeneous reservoirs, it is typically required to segment the wellbore with swellable packers to isolate sections with different reservoir pressure and/or fluid mobility, and the SL concept readily accommodates that. Also, since the subsequent stimulation relies on matrix acidization, the tool must ensure that fracturing pressures are not exceeded. The original limited-entry liner (LEL) technique dates to the early 1960s and was proposed for fracturing applications (SPE 530). Reviews by Somanchi et al. (SPE 184834) and Weddle et al. (SPE 189880) suggest that it is still widely applied for such purposes. In the late 1990s, Maersk Oil adapted the concept to effectively stimulate extended-reach wells in its North Sea chalk reservoirs on a large scale. Hansen and Nederveen (SPE 78318) refer to the technology as controlled acid jetting (CAJ). In the following years, the CAJ technique was implemented in more difficult formations such as a 0.1 mD chalk reservoir (SPE 144159) as well as in a tight, gas-bearing formation (SPE 123979). Balsawer et al. (IPTC 17611) designed multizone completions in ultralong wells in a giant field offshore Qatar, which comprised more heterogeneous limestone formations. Other field implementations have been described by Issa et al. (SPE 171779) for a super-giant reservoir offshore Abu Dhabi. Past deployments have concentrated on extended-reach wells with reservoir temperatures up to 210°F. Over the past year, ADNOC has significantly expanded the operational envelope of the Smart Liner concept. Fig. 2 summarizes the variation in completed reservoir length and average permeability for 80 well designs. Table 1 shows that reservoir temperatures vary from 140°F to 300°F.

Formation Pressure Inversion Method Based on Multisource Information

SummaryThe exploration and development of offshore oil and gas have greatly alleviated the tension of global oil and gas resources. However, the abnormal pressure of offshore reservoirs is more common compared with terrestrial oil and gas reservoirs, and the marine geological structure is complex, with the development of faults, fractures, and high and steep structures, which leads to the strong anisotropy of formation pore pressure distribution and uncertainty of pressure system change. In this paper, considering the corresponding characteristics of the randomness of the formation pressure prediction results in the Eaton equation for their respective variables, a formation pressure inversion method based on multisource information, such as predrilling data, bottomhole while drilling data, seabed measured data, and surface measured data, is established. On this basis, combined with the data of a well in the South China Sea, the variation law of the uncertainty of formation pressure prediction results under the conditions of predrilling data, measurement while drilling (MWD) data, and their mutual coupling is analyzed. The simulation results show that the uncertainty distribution of formation pressure prediction based solely on predrilling data shows linear accumulation trend with well depth, and the formation pressure inversion method based on multisource information can significantly curb the increasing trend of uncertainty when MWD data are introduced. Therefore, through the analysis of typical change patterns of monitoring parameters under normal/abnormal conditions during drilling, combined with the method of multisource information, the abnormal pressure information can be accurately predicted and inversed, which provides important support for wellbore pressure regulation under complex formation conditions.

Chain-based machine learning for full PVT data prediction

Building machine learning (ML) models based on pressure-volume-temperature (PVT) data is of paramount importance to capture trends and predict fluid behavior in a very heterogeneous and highly nonlinear thermodynamic system. PVT samples stored in an oil company database are often not complete and might be missing properties; both black oil and compositional. Before delving into building optimized fluid models, it is required to have a clean and structured PVT database complete with all the required properties. We present multiple novel algorithms developed to accurately predict a complete set of black oil and compositional properties within a PVT database. The proposed methodology consists of predicting properties in series, starting from a minimal set of data (black oil and compositional) and obtaining a complete set of data for all PVT samples. The order through which this is completed relies on benefiting from the existing data to predict missing data starting from the highest correlating data to the lowest. We also honored the physical nature of correlations between properties, and consequently, ranked properties for prediction as this leads to less error propagation. In addition, we have implemented data clustering prior to training ML models. Clustering is used to categorize the fluid samples into families based on the collective behavior of their different features, and hence, improve the quality of the PVT samples' properties prediction using machine learning. Several options are tested where clustering is performed using black oil properties only, compositional properties, or a combined set of black oil and compositional properties and the clustering scenario leading to the least prediction error is adopted. We have trained ML models to generically predict all black oil and compositional properties resulting from laboratory experiments, including molecular weights (MW) and mole fractions of heavy fractions (any set of heavy fractions) from the mole fractions of all the commonly available components up to C7+ and molecular weight of C7+. The massive data set used in this paper enabled comprehensive testing of the developed algorithms and provided striking accuracy of the predicted PVT properties; especially the compositional ones. Despite all the significant efforts shown in the literature concerning predicting PVT properties, the missing link is a systematic methodology to complete PVT samples' properties in a consistent manner. Furthermore, the focus in the literature is mainly on forecasting black oil properties; compositional properties are scarcely considered. Algorithms developed in this paper address these two limitations and are tested using a uniquely large data set available for onshore and offshore fields and reservoirs in Abu Dhabi. No previous algorithms, to the best of our knowledge, are tested on such a large data set. • Systematic, chain-based, methodology to complete PVT samples' compositional and black oil properties in a consistent manner. • Clustering to categorize fluid samples based on their thermodynamic behavior and reveal deep insights of these categories. • Application of the proposed algorithms for compositional splitting was a powerful illustration of the proposed algorithms. • Algorithms are tested using a uniquely large data set available for onshore and offshore fields and reservoirs in Abu Dhabi.

Complementarities and synergies with intermittent renewable energy, related issues - Burkina Faso cases studies

Pumped Storage Plants (PSP) offer opportunities for better water mobilization and to unlock the development of hydropower in Burkina Faso. The revolution in photovoltaic energy, which has greatly improved reliability and production costs, has opened up major prospects for the energy development of Sahelian countries with a very large solar energy deposit that has remained fallow for the time being. The lower production cost of solar energy makes it more attractive to mobilize water in offshore (outside rivers) basins and reservoirs in areas where there are few underground water resources and where flat land limits the construction of dams. This paper will develop these perspectives for a country like Burkina and the Sahel in general where access to electricity is one of the lowest in the world which, paradoxically, have a very large solar deposit and insufficient water resource mobilization.

Quantitative Characterization of Interlayer Interference in Multi-Layered Sandstone Reservoirs Offshore China

X oilfield is a typical multi-layer sandstone reservoir in offshore China. In the early stage, in order to obtain economic oil production, directional well was used to adopt a set of multi-layer combined production, which resulted in serious interlayer interference, water injection inrush and low reserve utilization. Based on the theory of single-phase unstable seepage flow and the theory of oil-water two-phase non-piston displacement, the author innovatively established a mathematical model of interlayer dynamic interference in multilayer sandstone reservoirs, revealed the influence law of main controlling factors such as permeability, viscosity, starting pressure gradient and reservoir type on interlayer interference, and innovatively formed a quantitative characterization theory of interlayer interference in multilayer combined oil production. The technical demarcation of offshore multi-zone combined oil production reservoir system is formulated and the recombination of oil field development system is guided.

Preliminary evaluation of the economic potential of the technologies for gas hydrate exploitation

Several trial productions of natural gas hydrate (NGH) on onshore and offshore reservoirs have been implemented, signaling the start of the stage of technology development for its industrial exploitation. Several methods for NGH exploitation have been proposed, but none of them has been verified applicable to the commercial exploitation of NGH. The applicability of a technology to NGH exploitation is subject to the evaluation of its economic potential, but unfortunately few relevant studies have been conducted. In this research, each exploitation technology for NGH is evaluated for its economic potential as referring to the break-even production rate with energy return on investment (EROI) analysis. Sensitivity analysis is also performed to specify the effect of each key factor, such as gas production rate, gas-water ratio, efficiency of thermal stimulation, injection-production ratio for the methods of chemical injection or CO2 replacement, on the standard EROI. The results obtained indicate that depressurization is the most promising method, because on it the lowest critical production rate would be required for commercial exploitation of NGH, ranging from 0.16 to 0.25 million m3/day/well. Comparing with other unconventional oil and gas, the commercial exploitation of NGH still relies on further technological breakthroughs, especially those for the improvement of production rate.