The Jurassic age Hanifa and Tuwaiq Mountain Formations are regionally established source rocks that charged majority of the oil fields in the region. These formations are comprised of dark carbonate mudrocks with high organic richness and dominantly calcite mineralogy. Several studies were conducted regionally to evaluate the potential of these Jurassic intervals as an unconventional play.
In April 2018, The Kingdom of Bahrain announced the discovery of a major unconventional resource in Khalij Al Bahrain basin following the production of light oil from Tuwaiq Mountain Formation. These results confirmed the viability of the Jurassic source intervals as an Unconventional asset. However, the nature and the location of the resource present a number of operational challenges in a region where development of unconventional resources is at its infancy. This instigates the need to address and tackle these challenges through innovative approaches to enable the effective appraisal and subsequently development of the asset.
This publication introduces the emerging unconventional play in Khalij Al Bahrain basin and discusses the adopted strategies to appraise and develop the asset. The areas for optimization considered include well design, drilling and completion, facilities and shallow offshore/onshore logistics.
The Hanifa and Tuwaiq Mountain formations are Jurassic in age (Figure 1) and consist of a mixed section of dark organic rich limestone beds. These formations are regionally established as the principle source rock that charged majority of the overlying Jurassic reservoirs in the region, and in Bahrain, the cretaceous reservoirs as well. These source rocks are the main targets of the recently discovered Khalij Al Bahrain (KAB) basin in Bahrain with initial resource estimates indicating potentially up to 80 billion barrels of unconventional oil and 14 trillion cubic feet of gas in place.
Location and Geological Settings
KAB basin is located in the eastern part of the Arabian basin straddling the area towards the east of Saudi Arabia, west of Qatar Arch and south of the Zagros fold belts. Majority of the basin today falls within the land bound shallow waters around the main island of Bahrain. Major fields in the area include Awali, Dukhan and Abu Safah which are likely to have been sourced from these Jurassic source rocks (Figure 2). KAB basin also lies in close proximity to the Jafurah basin which is a significant Jurassic unconventional play in Saudi Arabia targeting the same formations .
For mature oil fields with complicated reservoir architecture, reservoir surveillance is key to track reservoir performance. Reservoir surveillance may include various monitoring tools from complicated horizontal production logging tools down to regular well tests. One of the main surveillance methods is running formation pressure measurement tools such as Formation Pressure Testers (FPT) or as historically known to the industry, Repeated Formation Tester (RFT). This paper describes the use of this important tool integrated with production data to understand reservoir production and depletion behavior and hence support the Bahrain Field development plan.
A study was conducted on the Ostracod and Magwa reservoirs; complicated carbonate reservoirs in the Bahrain Field. The Ostracod Zone is a sequence of inter-bedded limestone and shale in the upper Rumaila formation of the middle Cretaceous Wasia group. It is over 200 feet thick and consists of three main units: B0, B1, and B2. The Magwa reservoir is the lower member of the Rumaila Formation. It is 120 feet thick and conformably underlies the Ostracod reservoir. It consists of three main units: M1, M2, and M3.
The main objectives of this study are:
Evaluating pressure depletion from the initial reservoir pressure for each unit in both reservoirs, which defined the existence of flow barriers in this inter-bedded complicated carbonate. Evaluating the relationship between pressure depletion in each unit and the spacing between offset wells to the FPT location. Evaluating the Ostracod/Magwa pressure depletion per unit with time. Linking the pressure depletion to the cumulative production from the area offset by the FPT data.
Evaluating pressure depletion from the initial reservoir pressure for each unit in both reservoirs, which defined the existence of flow barriers in this inter-bedded complicated carbonate.
Evaluating the relationship between pressure depletion in each unit and the spacing between offset wells to the FPT location.
Evaluating the Ostracod/Magwa pressure depletion per unit with time.
Linking the pressure depletion to the cumulative production from the area offset by the FPT data.
The results of this study helped define the depletion risk on the future infill opportunities in such complicated reservoirs. It also helped in locating highly depleted units and determining the optimal locations for the new infill wells.
The Light Oil Steam Flood (LOSF) is proposed to increase the recovery from Mauddud reservoir in Bahrain Field. Mauddud has been on gas injection since 1938, yet residual oil saturation is still high in the gas cap due to its oil wettability. Several core lab studies were conducted confirming the high oil saturation in the gas cap. Steam flood core lab experiments were conducted recently and confirmed the residual oil saturation could reach to less than 10%. The thermal pilot project in Mauddud has gone through the following stages: The first pilot started in 2013 and operated for 2.5 years: It has one horizontal well in the gas cap, one vertical producer, four vertical injectors with three Temperature Observation Wells (TOWs) clustered around one of the injectors. First pilot performance was assessed and confirmed in reducing the residual oil in the gas cap by distillation and wettability alteration. Second pilot was designed and initiated in 2016 to assess the economic viability for full field expansion.
The first pilot started in 2013 and operated for 2.5 years: It has one horizontal well in the gas cap, one vertical producer, four vertical injectors with three Temperature Observation Wells (TOWs) clustered around one of the injectors.
First pilot performance was assessed and confirmed in reducing the residual oil in the gas cap by distillation and wettability alteration.
Second pilot was designed and initiated in 2016 to assess the economic viability for full field expansion.
Throughout these stages, production monitoring, logging, core studies and simulation studies have been carried to understand the LOSF mechanisms to increase Mauddud recovery from the gas cap.
This paper presents the evolution of pilot design concepts and simulation of the thermal recovery in Mauddud. It also study and assess the well configurations and pilot operating strategies designed for the thermal pilots. A sector model was constructed and calibrated, then used to select a well concept for the LOSF pilots. Seventeen different pilot concepts were considered during the selection process. The well configuration and operating strategies were driven to observe a quicker steam response in the first pilot. A number of sensitivities were conducted to develop a better understanding of the effects of the various reservoir factors.
A comprehensive study was then carried out to recommend a phase development approach for full-scale field development and establish a methodology for a full-field LOSF forecast. Full Field compositional model was built in thermal reservoir simulator and was then successfully history matched with seven components equations of state (EOS). A phased development approach was then proposed for full-scale field development. The initial development will focus on the mid-dip areas with higher remaining oil saturations and a thicker oil column. After establishing production in the mid-dip flanks, development could proceed to the crestal areas, which have lower oil saturations and would likely result in higher steam/oil ratios (SORs).
The sandstone facies of Wara formation designated as Ac zone in the Bahrain Field belongs to the Wasia group of the Middle Cretaceous age.
The reservoir has been characterized in three distinct geographical areas of sand distribution based on varied depositional systems, resulting in sands with differing orientation, texture and thickness. The reservoir varies in thickness between 5 and 60 ft and is composed of a series of discontinuous high porosity, high permeability sandstone lenses, sealed above and below by thick competent marine shales.
This paper addresses the variability of the reservoir and the connectivity with the underlying Mauddud reservoir which consequently determined the drive mechanisms.
The original oil in place of Wara sandstone was calculated deterministically using a 3D geological model and incorporated both Geophysical and Petrophysical models. Initial water saturation was calculated from capillary pressure data with net sand cut offs applied. The discontinuity of the sands has resulted in individual sand bodies with variable oil water contacts. Thinner sand bars and channels in the northern area of the Bahrain Field produce by depletion drive. Juxtaposition with the underlying Mauddud reservoir occurring across the faults allows communication with Mauddud gas cap in the Central area which results in the gas drive. Water drive is the main mechanism in the South channel.
Recent log data acquired from new wells has improved our knowledge of this reservoir and explains the different oil-water contacts with the varying drive mechanisms. This improved understanding has resulted in a new development strategy to maximize recovery with infill drilling and possibly Enhanced Oil Recovery (EOR).
The Bahrain Oil Field was the first oil discovery in the Gulf Region in 1932 and is now in a mature stage of development. Crestal gas injection in the oil bearing, under saturated, layered and heavily faulted carbonate Mauddud reservoir has continued to be the dominant drive mechanism since 1938. Thirty eight 40 acre 5-spot waterflood patterns were implemented from 2011 to 2012. These patterns were located in both the South East and North West part of the Mauddud reservoir with a maximum injection rate of 80,000 bbl/day. With less than 10% PV water injected as of December 2012, premature water breakthrough was observed in most of the producers. Rapid water breakthrough in Mauddud A (Ba) is attributed to presence of high permeability vugs and layers resulting in water cycling and poor sweep in the matrix leaving bypassed oil. Following recommendations from the 2013 partner Peer Assist, the South East and North West waterfloods have been converted from pattern to peripheral with downdip wells providing water injection. Peripheral re-alignment has arrested the production decline, reduced water cut and stabilized production.
Surveillance data such as bottomhole pressure data, production logs, reservoir saturation logs, temperature logs and tracer data form the basis of understanding waterflood performance. Additionally, an array of analytical tools were used for diagnosis and analysis. Amongst the diagnostic tools, the Y- function helped to understand water cycling and sweep; the modified-Hall plot assisted in understanding the high-permeability channel or lack thereof and the water-oil-ratio (WOR) provided the clue on fluid displacement. Additional plots such as the "X" plot, decline curve, Cobb plot, pore volume injected vs. recovery, Jordan plot, and Stagg's plot were generated to gain insight on the waterflood.
Based on the waterflood analysis, a field study was initiated in December 2016 by shutting more than 80% of water injection followed by complete shut-in in September 2017. The purpose was to reduce the water cut, improve production taking advantage of gravity drainage effect of gas injectors located up dip of waterflood areas. The implementation of water injection shut-in is still ongoing in the Bahrain Field and pressure/production performance is being closely monitored. Improved production performance is observed following water injection shut-in.
This study underscores the importance of modern analytical tools to diagnose and analyze waterflood performance. This understanding also paves the way for much improved learning to take appropriate actions and help devise long-term reservoir management strategy.
The unexpected response of the Mauddud water flood project led to a detailed review of the petrophysical and geological aspects of this mature cretaceous carbonate reservoir. With almost 2,000 wells, more than 1,000 of which were recently drilled and three cored, the review assessed an extensive data base of openhole, production, saturation log, and historical geological data. The findings resulted in an improved understanding of this reservoir, which historically had been described both as homogenous - fractured and heterogeneous - layered. An understanding of Mauddud's key geological features, their formation, and a link to the observed petrophysics provided the key to developing an innovative permeability transform from resistivity logs, which explained the reservoirs response to the water flood project. With production permeability up to fifty times the measured matrix permeability from core, porosity log derived permeability had failed to reflect the fluid production observed. The adoption of a saturation and production based method provided a useable permeability profile that appeared to explain the observed well and pattern production behavior of the water flood. The new permeability profile also explained both historical fluid behavior and other Enhanced Oil Recovery (EOR) projects, and has since been universally adopted for the reservoir. The permeability estimation technique, which uses resistivity log data, was tested in another infield reservoir with success, and it is thought that the technique has general applicability across many Middle East carbonate reservoirs.
The Bahrain Field, being the first oil discovery in the gulf region in 1932, is now in a mature stage of development. Crestal gas injection in the Mauddud reservoir has continued to be the strongest driving mechanism since 1938. Over the last five years, gas injection and fluid production rates have grown three folds with expanded drilling, workovers, and high volume lift activities. However, there are significant opportunities to increase oil production and optimize gas injection.
An Immiscible-Water-Alternating-Gas injection (IWAG) process was carried out on two composite samples extracted from the Mauddud reservoir of the Bahrain Field. The resulting production and pressure profiles were history matched by using hysteresis and three-phase relative permeability modeling options. Representative relative permeability and capillary pressure curves with the associated hysteresis and three- phase relative permeability parameters were obtained by history matching the experimental IWAG flood results. The history match was carried out by generating the hysteresis parameters and relative permeability curve sets. Experimental results, including two-phase water/gas flood steady state and unsteady state results, were honored to the degree possible. In both composite samples, the IWAG process showed incremental recovery compared to the base case water and gas injection cases. The incremental recovery obtained (above 10% PV) was largely due to the reduction of gas relative permeability during three-phase flow. A maximum trapped gas saturation of 23% was used to history match the core-flood results.
A sector model of the Mauddud reservoir was run using the relative permeability and hysteresis model parameters obtained from the history matching of the composite core-floods. A water and gas flood base case was run and compared to the IWAG sequence. The IWAG process showed incremental recovery compared to the base case water injection. In the up-dip pattern where the water saturation is low, IWAG recovers 3% more than base case gas injection, while gas injection recovers 5% more than the IWAG sequence in the down-dip pattern where water saturation is higher.
The objective of introducing the Immiscible Water Alternating Gas process (IWAG) in Mauddud was to reduce gas production by controlling the mobility during the three-phase flow. Incremental oil, compared with gas and water injection was also to be evaluated. Three IWAG pilots were introduced after an extensive study on optimum locations. Two inverted 5-spot patterns and one line drive pattern were selected; each pattern is around 40 acre spacing, targeting Mauddud B interval. The original Water Alternating Gas (WAG) ratio was designed to be 1:3 (Water: Gas) and the WAG period was originally designed to be from three to six months based on simulation work. WAG ratio and duration optimization were subject to performance. After one year of cyclic injection, both inverted 5-spot patterns showed lack of response to the WAG cycles. In one of the two latter patterns, the water cycles critically affected oil production. In the line drive pattern, the WAG cycles initially showed a favorable response. After one year of injection, water and gas overcame oil production, leading to higher oil decline and the termination of the pilot due to confinement and operational issues.
The Bahrain Oil Field is located in a desert environment in the south-central area of the Kingdom of Bahrain and spans approximately 25% of the island. The Bahrain Field was discovered in the early 1930s and is recognized as the first oil field developed in the Arabian Gulf.
Recently, Tatweer Petroleum introduced advanced Unmanned Aerial Vehicles (UAV), also known as (Drones), to address the unique needs of its daily operation by providing a safe, efficient, and cost-effective maintenance and inspection solutions.
This paper demonstrates the valuable benefits of utilizing UAV (Drones) in the oil and gas industry in three main areas: ‘Security, Surveillance, and Emergency Response,’ ‘Inspection and Maintenance,’ and ‘Surveying and Mapping.’
Under the Security and Surveillance front, Tatweer Petroleum is facing operational safety issues and security threats that require real-time response solutions, and the need to provide rapid, precise, and reliable situational awareness. Tatweer’s Drones support the Security team with dynamic perimeter surveillance, intruder alerts, and critical equipment and process monitoring. Additionally, the Drones are used to support the emergency response team as a professional tool for rapid aerial incident investigation, evacuation, monitoring, and remote hazard detection.
Preventive maintenance inspection is another application area where Drones can play a vital role. This is especially true when it comes to inaccessible operational assets due to their physical location (e.g. overhead power lines insulators), sheer magnitude (e.g. solar cell farm), or an inherent process hazard (e.g. flare stacks). Airborne cameras with advanced spectral imaging technology and powerful magnification optics can capture, analyze, and identify particular anomalies such as oil or gas leaks and pre-failure overheats, and provide vivid close-up images of fatigued structures and micro failures in plants and assets. This is a great cost-effective and efficient method for inspection and failure prevention.
Surveying and mapping an industrial environment is time-consuming, difficult, and often dangerous. Tatweer Petroleum used the Drones to allow surveyors and mappers to collect unlimited aerial data with precise measurements, while saving time, money, and manpower. It also provides premium processing and analytics capabilities to support critical processes such as stock pile volume measurements, terrain mapping, site planning etc. The Drones are preprogrammed to automatically cover any particular area in the Bahrain Field. The survey data produces highly accurate, best-in-class orthophotos and digital elevation models.
AL-Muftah, Ali (Tatweer Petroleum)
The Bahrain Field is characterized by large lateral and vertical variations in fluid properties, with oil gravity ranging between −9 and 80 °API. The lower API crudes are encountered mostly on the structural flanks and within the upper reservoir units, while the highest API crudes are condensates from deeper formations such as Hith and Arab. The deepest reservoir is the gas-bearing Khuff. It has 50 °API condensate and forms a separate fluid type from the rest of the Bahrain Field.
The objective of this paper is to derive a single compositional predictor for the entire range of crude gravities. Excluded from this unified model are bitumens from Aruma and Khuff condensates, which are compositionally different. One outcome of this study was to predict the reservoir fluid as a function of well test Gas Oil Ratio (GOR) and API gravity by mathematical recombination of averaged data from abundant well tests across the Bahrain Field. A strong trend of methane fraction in the reservoir fluid versus saturation pressure has been observed, and thus it has been possible to construct the recombined reservoir fluid and then predict saturation pressures, Formation Volume Fraction (FVF), and viscosity. This fluid model was used to initialize compositional models for gas plant evaluations, miscible flood evaluations, and to determine the maximum GOR at which saturation pressure equals reservoir pressure. Another outcome of the unified fluid model was to construct a reservoir fluid composition given a target saturation pressure and API. This information is used to construct representative fluids for laboratory synthesis of crudes and gas for live oil experiments.
As part of the process, a number of quality checks were constructed to determine if the fluid encountered is in range of historic produced crudes (e.g. contamination by air or lift gas) and enable construction of fluids for reservoir simulation.
One of the critical processes in managing oil field development is to effectively manage the Annual Work Program and Budget ("AWPB"), a program that contains a company's planned projects, costs, and oil recovery projections, and to execute this AWPB to meet company objectives and goals. Although creating an AWPB in an oil company is a challenge in and of itself, executing the plan with effective control represents a bigger challenge that is the key to achieving success in such a dynamic environment. To address this challenge with an effective tool, "Tatweer Pulse" was developed as a strategic dashboard that brings the pulse of the field to the decision makers' fingertips. Tatweer Pulse is a system that monitors the AWPB performance in terms of initiating and tracking field activities, communicating information between stakeholders for effective decision making at any given point, promoting consistency across the organization, improving employee efficiency, and enabling executive management to implement real time planning and change of strategy if needed. We have successfully completed and tested the pilot phase of Tatweer Pulse, and are currently defining the scope and setting targets for the second phase.