Most oil fields worldwide are stored in carbonate rocks, which vary in rock and fluid properties. Heterogeneity, thickness, and depth play vital roles in the selection of specific acid stimulation to improve the productivity and injectivity of the wells from near-wellbore damaged formation resulting from overbalance drilling. This paper describes the integrated workflow that guides petroleum engineers in the selection of optimum acid stimulation techniques and technologies for a specific field. Specifically, this work discusses the stimulation strategies in the form of a stimulation workflow that considers various aspects to achieve the stimulation objectives. The stimulation objectives are also streamlined for the well objectives, which mainly consider the well completion approach. Considering the well completion and well objective, the stimulation strategies highlight the conveyance selections, fluid selections, and the methodologies. Guidelines are provided as examples for fluid specification. Some comparisons of the stimulation fluids are also shown to consider the advantages and disadvantages of each application. Example simulation and case studies show various applications in UAE. Numerous new technologies and different acid types have been tested worldwide on different carbonate rocks whereas very limited information exists on a tailored acid stimulation workflow that can be fit to the needs of a specific field. The developed workflow is an integrated holistic guidance based on worldwide best practice of acid stimulation and can facilitate and guide technical expertise for production and cost optimization in different oil and gas fields. The latest stimulation technologies are highlighted for the reference on the case studies.

Development and application of enhanced oil recovery (EOR) processes in layered heterogeneous carbonate reservoirs has been considered a real challenge and a difficult endeavor. A multi-layered heterogeneous carbonate oil reservoir was screened and selected as a good candidate to investigate the feasibility of Water-Alternating-Gas (WAG) process using both hydrocarbon and non-hydrocarbon gases. An integrated reservoir characterization model and the pertinent transformed reservoir simulation history matched model were developed. The main objective of this work is to define the development process that could provide the maximum ultimate recovery factor of more than 70% IOIP. This could increase the total technical reserves by 30 % over the reserves based on classical water flooding reserves. The attained results are used to conclude that the life of the field could be extended and almost doubled. The results also indicated that the best technical development process that provides maximum ultimate recovery factor of more than 70% was the H 2 S-WAG development process. The enriched-WAG development scheme can be designed to give an equivalent ultimate recovery factor by enriching the gas. The N 2-WAG development process gives a relatively poor recovery factor. This is the lowest of all the Non-hydrocarbon Gas Injection (NHGI-WAG) development processes investigated.

Reservoir management is a data driven process with an objective to achieve an optimum ultimate oil recovery. It is fundamental to obtain a proper understanding of well and reservoir performance, which can only be built based on the acquired data. Data acquisition in brownfield has been a significant challenge due to the obsolete control system, accessibility and workflows. Daily well changes is one of the key pieces of data required in routine allocation, well performance analysis, as well as simulation model updates and hence development plans. There are two major types of acquired data in the presented giant offshore brownfield, which are manually measured by operators and automatically recorded data through available SCADA system. A comprehensive data analysis has been conducted based on historical production data and reservoir surveillance data to spot the gaps and identify the opportunities for future improvement. Gaps in daily well changes data have been observed from both manually and automatically acquired data. It has been summarized into two main categories, which are data inaccurate and data missing. The inaccuracies are mainly from improper use of well change event types, inaccurate timing of data acquisition and malfunctioning of SCADA systems. Missing data includes loss of manual measurement records and insufficient utilization of SCADA data. The paper presents real examples of all these findings and a proposed workflow to enhance the data acquisition process. The concise and explicit workflow is one of the most efficient approach to tackle the hardware and manpower limitations. The importance of daily production events could not be over emphasized. Specific actions to bridge the identified gaps are crucial to achieve a sound reservoir management, maintain the sustainability, and ensure an optimum oil recovery.

Carbon dioxide capture, utilization and storage (CCUS) has been recognized as a key technology to reduce CO2 emission. Among various CCUS technologies, CO2 enhanced oil recovery (EOR) has been widely implemented at an industrial scale in the E&P sector. However, it is well-known that CO2-mixed oil would cause asphaltene precipitation resulting in flow assurance troubles. Therefore, more advanced asphaltene-risk-managing technology can be an enabler to improve robustness of CCUS projects. This paper presents a case study for a comprehensive series of asphaltene flow assurance pre-risk evaluation in Arabian Gulf Carbonate Oil Field at where the CO2 EOR is recognized as one of the highest potential technologies for full-field implementation. At first, sampling location was carefully selected considering the target reservoir's feature because the reliability of asphaltene study highly depends on sample representativeness. After the QA/QC of collected sample, asphaltene onset pressures (AOP) were measured at multiple temperatures under the CO2 mixing conditions in a straightforward experimental-design optimizing manner so that not only the evaluation accuracy could be improved but also the experimental cost could be minimized. The AOP measurements showed clear potential risks associated with CO2 injection. Subsequently, the numerical model analysis was conducted with Cubic-Plus-Association (CPA) EoS model to identify the risk area during CO2 injection. The analysis suggested that a risk would be caused at not only near-wellbore region at the sampling location but also tubing section / surface facility, furthermore, more seriously at the deeper location of target reservoir. Finally, CO2-induced asphaltene formation damage risk was investigated from the viewpoints of precipitated asphaltene particle size and pore throat size in the porous media. As a result, the clogging risks by CO2-induced asphaltene were estimated high in the target reservoir. By virtue of the above comprehensive series of pre-risk evaluation, the asphaltene flow assurance risk associated with CO2 injection was identified field-widely. The evaluation findings suggested moving on to future actions such as more detailed formation damage risk evaluation and mitigation plan development. The phased approach for evaluating asphaltene flow assurance risk and the reverse engineering of sampling operational design from the experimental design made a worthy demonstration to reduce unnecessary cost and time while obtaining the key information to drive the project. The procedure in this work can contribute to establish a subsurface part of guideline for CCUS from viewpoints of asphaltene flow assurance risk evaluation.

To enhance oil production (EOR) in tight carbonate oil reservoirs, gas EOR can be a promising option from injectivity viewpoints compared with water-basis chemical EOR. CO2 is the most attractive injectant with higher recovery factor expectation while responding to the recent decarbonization demands; however, CO2 is also known to accelerate asphaltene flow assurance risks. In actual fact, the previous work revealed a high asphaltene flow assurance potential risk for CO2 injection. Therefore, a further pre-risk evaluation case study was conducted to extract adequate type of potential injection gas among CO2, enriched gas, and lean gas. This study focused on subsurface gas-induced asphaltene risks in an offshore heterogeneous oil field showing unstable asphaltene colloidal instability index (CII=2.2), where a crestal lean gas injection has been applied without any asphaltene issues. A single phase bottomhole sample was taken from appropriate candidate well keeping representative reservoir fluid in a clear asphaltene-gradient field: i.e., lesser asphaltenes in shallow depth but more in deeper section. As a result of this study, no asphaltene onset was detected from original reservoir fluid while asphaltene onset pressures (AOPs) were detected from mixture of reservoir fluid and CO2 or enriched gas or lean gas at two temperatures representing reservoir and wellhead conditions. Experimental gas mixing ratios were carefully designed to distribute the AOPs broadly in operating pressure range: from in-situ reservoir and near wellbore to bottomhole, for securing higher numerical model accuracy by avoiding data extrapolation. A numerical model, calibrated with experimental outputs, predicted risk magnitude by reservoir depth. A comparative analysis revealed higher asphaltene precipitation risks in CO2 injectant than enriched gas and lean gas. Finally, asphaltene particle/aggregate size were discussed for formation damage risks. The visually measured asphaltene solid particle size varied from 1-10 μm for CO2 injection and 1-4 μm for enriched gas injection while no visible for lean gas. From the past injection water quality analysis, the reservoir has threshold particle size between 0.5-1.0 μm to cause plugging. Therefore, it was concluded that risk of asphaltene-induced formation damage is lower in enriched gas injection compared with CO2 injection. In general, higher oil recovery is expected by order of CO2, enriched, and lean gases. In conclusion, even CO2 EOR is being attractive rapidly from decarbonization viewpoints, the study highlights an importance of balancing business case opportunity and risk from the aspect of injection gas-induced asphaltene flow assurance potential risks.