The objective of this paper is to share learnings from the Okan field, highlighting successful strategies adopted to mitigate reservoir and operational decline almost 8 years without producer drilling or major rig workovers. Value gained is quantified to show that over a third of the current Okan production is tied to strategies adopted during the period of interest.
Details of the different wellwork methodologies are provided to communicate how value was maximized using minimal cost. Key strategies adopted that have created the Okan success story over the period of interest include the jacket-centric rigless wellwork approach which has resulted in a drop in overall wellwork costs as multiple wells on the same jacket are worked over in one mobilization. The use of interwell gas lift systems for isolated jackets unlocked reserves that would otherwise be uneconomic because of costly pipelay. In addition to enhancing production from wells requiring gas lift, the conversion of idle oil line conversions to gas supply lines for gas lift ensured available facility assets are utilized, bringing pipelay savings as well as production gain. Also, taking full advantage of the Okan Gas Gathering and Compression Platform, production from reservoirs with high GOR has been optimized, resulting in oil and gas gain without routine gas flaring. Challenges encountered and lessons learned are also shared in this paper.
As a result of the strategies shared in this paper, the current Okan production is over 30% higher than what it would have been without the deployment of these strategies highlighted. The same strategies can be transferred to other assets to obtain optimum value in these times of low commodity prices.
Ogbuagu, Frank (Chevron Nigeria Limited) | Afolayan, Femi (Chevron Nigeria Limited) | Esan, Femi (Chevron Nigeria Limited) | Obot, Nsitie (Chevron Nigeria Limited) | Adeyemi, Ganiyu (Chevron Nigeria Limited) | Okpani, Olu (Chevron Nigeria Limited)
This paper summarizes the strategy adopted in the development of two thin oil rim reservoirs in Okan Field, Offshore Niger Delta, Nigeria.
Its objective is to elucidate the strategy, engineering analyses, subsurface assessment and production procedures set in place to optimally develop the reservoirs.
Both reservoirs have oil thickness of <30 ft with gas thickness of >100 ft. The adopted development strategy for the two reservoirs involves the drilling of 4 wells, 2 in each reservoir, to drain the remaining oil reserves, prior to gas development.
Because of structural and fluid contact uncertainties, soft landing was incorporated into the well designs. Shale-to-shale correlation was used for accurate horizon depth prediction and detailed simulation models with local grid refinements were employed to determine optimum well orientation, landing depth, lateral length and aquifer properties. Details on their use to maximize value are shared.
While drilling, Azithrak™, a Baker Hughes tool, was used in geosteering the lateral well section to determine distance of well to nearest conductive zone as part of the oil-water contact tracking. All available data - logs, cuttings, reservoir pressures and production data - was incorporated and used to validate fluid contacts data because of the impact of landing depth relative to the fluid contacts on oil recovery. Simulation results and operational constraints were used to set acceptable production limits to ensure delivery of target reserves.
All the four wells have been successfully drilled and completed, with the wells landed successfully within the thin oil column, at the optimized distance from the fluid contacts, with the wells producing at <0.55 percent water cut. Initial production performances of the four wells are in line with static and dynamic assessment forecasts.
Lessons learned and challenges encountered during this development are also captured in this paper.
The application of appropriate tools and processes is necessary to ensure reliable and accurate forecasts of hydrocarbon reserves that will enable more informed capital management decisions on projects. This becomes even more critical considering the tight budget environment which most operators face in the oil and gas industry.
Sustaining oil production in brown fields comes with a myriad of challenges because the once blocky and apparently homogeneous sands are now compartmentalized due to differential depletion, water influx / poor waterflood performance and the emergent effects of erstwhile salient features like small channels, sub-seismic faults, baffles and heterogeneities. These truths get revealed with time as we know more about the reservoirs / fields through: state-of-the-art seismic data acquisition and/or reprocessing, formation evaluation and production data mapping. This information also helps to finetune our simulation models.
The implication is that viable new drill opportunities have now become more difficult to identify and adequately plan because the targets are no longer as evident or "stacked?? one on top of another. Due to the prevailing high cost environment, a new drill opportunity today more than ever before will require multiple targets in order to pass the economic hurdle.
Accurately forecasting these multiple streams is critical to meeting the overall project objective. The 4kast-Pro™ software has been built to provide a structured approach to developing production forecasts which is critical to achieving world-class reservoir performance and return on investment.
Afsari, Meisam (Iranian Offshore Oil Company) | Amani, Mahmood (Texas A&M U at Qatar) | Razmgir, Seyed Ahmad Mohsen (Iranian Offshore Oil Company) | Karimi, Hassan (Schlumberger) | Yousefi, Saman (National Iranian Drilling Company NIDC)
Drilling through subjected mature offshore oil field is made more challenging by problems arising from wellbore instability, mud losses, excessive cutting, tight hole, stuck pipes and kick/flow zones for last few years. These problematic layers have caused quite a significant NPT (non productive time) during drilling.
For better understanding of factors causing wellbore instability problem and to predict mud weight window to be used for future wells, construction of mechanical earth model (MEM) was essential.
Mechanical Earth Model (MEM) is a numerical representation of the state of stress and rock mechanical properties for a specific stratigraphic section in a field or basin2.
In this study main drilling problems for each drilling interval in this field were described afterward different stages for construction an 1D Mechanical Earth Model (MEM) for the field was established. It was then demonstrated that how 1D MEM could be used to predict and prevent the common instability problems encountered during drilling.
For making MEM different sources of data including, drilling data, formation evaluation data, well testing, etc were used.
After making MEM for the field, safe and intact mud weight window was determined and according to that, suggestions for optimum mud weight for stable borehole on each interval was made.
MEM for this field can now be used to predict not only the safe mud weight window and possible drilling hazards, but can also be used for studies like reservoir compaction, sand production, and perforation stability and so on.
The subject field is located in central part of the Persian Gulf and its structure is result of salt tectonic. On this domal structure, several faults trends of NW-SE are visible on the seismic data which have produced some grabens. Most sections of the stratigraphic column are dominated by carbonates with thin lamination of shales and evaporate except one sandstone layer. 3D geological view of the field is shown in Figure1.
This field has been experiencing some drilling problems for last few years. Mud losses, excessive cutting, tight spot, stuck pipes, and kick/flow zones are some of the commonly occurred problems. Some stratigraphic levels have been quite difficult to drill through, which has caused quite a significant NPT (non-productive time). In some cases, side-track holes had to be drilled from the original hole. Generally, it is not so easy to predict what kind of problem the well would get into.
Minimizing the risk of problems related to geomechanical properties requires understanding the geomechanics of well construction and field, In order to be able to address the drilling problems and propose the solutions for the future wells which could optimize drilling and production performance of the subject field.
Here the methodology of building a MEM is presented. Generally geomechanical model relates dynamic elastic properties to static equivalents. These elastic static properties are then used to characterize formation strength and in-situ stress4. The MEM consists of depth profiles of elastic or elasto-plastic parameters, rock failure mechanisms, geologic structure, stratigraphy, well geometry, earth stresses, pore pressure and stress direction. After construction, this model can be used to identify geomechanical problems and to consider those problems for planning future wells.
Ifediora, Emmanuel (Addax Petroleum Development Nigeria Limited) | Ibrahim, Charles (Addax Petroleum Development Nigeria Limited) | Ekeke, Davis (Addax Petroleum Development Nigeria Limited) | Nwaochei, Francis (Chevron Nigeria Ltd.) | Ogugua, Emeka (Chevron Nigeria Ltd.) | Ene, Emeka C. (Oildata Wireline Services) | Orumwese, Sylvester (Oildata Wireline Services) | Idedevbo, Kingsley (Oildata Wireline Services)
Electric line remedial work such as through tubing perforation has been successfully carried out in most vertical/deviated wells. However, in high angle/horizontal wells it has become a major undertaking due to inability of the gravity-assisted, electric line to convey perforating guns to angles greater than 65°. With this electric line limitation, the options available for deploying the guns are limited to wireline tractor and e-coiled tubing since most through tubing perforation are done in real time. Apart from space constraint at the wellsite and cumbersome logistics, the main set back with the e-coil is its unavailability, while the tractor has high operational cost. This paper outlines the successful perforation of horizontal wells in the Niger Delta while addressing the operational issues encountered.
The first case history is Addax ORW-11H, a horizontal well planned to have the lateral section slimmed down to 6 in. hole. After successfully drilling the hole to target depth (TD), a 6-in. hole-opener was deployed on 3½ in. drill pipe to condition the well before running the 4½ in. liner. In an attempt to re-run the hole-opener, the bottomhole assembly (BHA) got stuck 20 ft off target depth. After several unsuccessful attempts to recover the BHA, it was decided to perforate the 3½ in. drill pipe to provide a conduit for production. The challenge was deploying the gun at 90°deviation, correlating and perforating on depth without e-coil. This was overcome by using an intelligent memory correlating and perforating tool to perforate the drill pipe and communicate with the reservoir. On completion, the well delivered 1,400 bopd with 0% water cut.
The second case history is Chevron Okan Well Y, which was drilled and completed as a horizontal gravity waterflood injection well. The initial 20,000-bwpd water injection began to drop and later quit due to sand accumulation and plugging. After an unsuccessful sand cleanout, the proposed remedial action was to add 40 ft of additional perforations shallower in the target reservoir to provide access for the desired injection rates for the well and help increase recovery. Initial attempt to run electric line to TD failed due to inclination of over 77°, but the well was later perforated successfully using the same novel technology with significant cost reduction.
Okan field is one of the oldest fields being developed in offshore Nigeria. Geomechanics challenges with further development include drilling through severely depleted shallower reservoirs, high-angle penetration through sloughing shales, and horizontal wells. Significant downtime due to tight hole, packoff, and stuck pipe was experienced in several wells drilled recently, which resulted in significant extra capital expenditure.
After reviewing relevant data from the field, a 1D Mechanical Earth Model (MEM) was established. It was found that the Okan field generally has a benign stress environment without clear maximum horizontal stress orientation, indicating no significant horizontal stress anisotropy. Rock mechanical properties were calculated with wireline/LWD logs based on a Rock Mechanics Algorithm (RMA) that is closely linked to Chevron's worldwide rock mechanical property database. Consequently, even when there were no core test data available to calibrate RMA predictions directly, the log dataset provided the means to estimate reliable formation mechanical property values that are consistent with Chevron's worldwide database. Furthermore, the entire MEM was calibrated against offset data, resulting in a high degree of confidence in the predicted values. A lookback on the drilling history indicated that drilling problems were mostly caused by low surface mud weights for high-angle wells, combined with incorrect ECD management. As such, recommendations on downhole mud weight and well design were made to mitigate future wellbore stability related problems. Wellbore collapse mud weights were predicted and recommended for new wells based on this study. Drilling experiences review of the newly drilled wells indicated that wellbore stability related problems were significantly reduced, proving the efficacy of the MEM.
Organizations operate to their optimal capacity in an environment that is stable. Social-economic instability or political violence can adversely affect the growth and productivity of an organization.
Chevron Nigeria Limited/Nigeria National Petroleum Company (NNPC) explores for petroleum in Niger Delta area of Nigeria, for about three decades. The past three years have recorded ethnic unrest and violence that have never been experienced.
Chevron's policy of maintaining a Mutually Beneficial Relationship with Host Communities has encouraged social development. In this regard, Chevron worked with communities to provide basic social amenities that were lacking in the area such as schools, educational equipment, hospitals, portable water and electricity.
The recorded inter-ethnic violence have made people homeless, villages burnt down, diminished food production, no logistics for food distribution, no potable water supply, properties lost, human suffering especially women and children, lives lost and problems of orphans now and in the future - the fabric for community participation severely disrupted. The war like situation has resulted in a crisis with people needing help, but assistance never came. Hostage taking is common.
Chevron, a neighbour, reacted to the emergency by providing shelter for the homeless, food, water, clothing, medical supplies and personnel to treat the wounded and illness. Spiritual and emotional support was made available to those in need. Displaced people whose homes and property have been burnt were airlifted from the disaster area to a safety. In a single operation 2,360 people (two thousand, three hundred and sixty) were evacuated from the disaster area to Warri.
This paper reveals how Chevron reached out to people in times of crisis and recommends and inter-sector collaboration between credible organizations in achieving peace and sustainable development in the area.
Chevron's achievements and growth in Nigeria would have been impossible, if its operation were conducted in a hostile and war-torn environment. Chevron began operation in Nigeria shortly after the country became a sovereign nation in 1960. Her present position as a major player in Nigeria's oil industry was established in 1962 when it discovered the Okan field, the country's first successful oilfield. Many other successes have followed since this initial discovery, with company's production rising annually. Most of the recorded successes occurred from 33 producing fields both East and West of the Niger Delta.
Over the past 38-year period, the successes recorded have been possible through the partnership that the company has forged with the government and the people of the country.
In the past three years, however, we have seen ethnic unrest, and violence that have not been expeienced in the history of our existence in the area. Ethnic conflicts present a war scenario that calls for emergency response. We believe that it is the responsibility of all to come to the rescue of victims of `war'.
It is a fact that there have been clashes between the various ethnic groups in the Niger Delta. Often we read in our newspapers that some youths from one group have sacked an enemy village, burnt it down with associated fatalities. These ongoing and bitter wars, in effect, are civil wars. My experience of the effects of these conflicts in Warri area are similar to those observed in other regions of the world where civil or political conflicts result in war.
This program is operational in Chevron Nigeria Limited and was introduced as a framework for integrating risk assessment within a risk management system. Also, the risk assessment program was developed to provide a process for rapid screening of risk in order to focus attention on risk levels that need to be eliminated or minimized. The article examines the principles and techniques of risk assessment and risk management, and it illustrates their applications. It also describes how these techniques are used to prioritize decisions in preparing an effective ranking of risks within Chevron Nigeria offshore facilities. Risk assessment flowcharts, hazard identification, and risk assessment checklist were generated as a rapid guide to evaluation of the level of risks and to decide which risks would need more detailed analysis. The hazard identification has the following parameters as areas of concern Viz.: - Hazardous substances, Mechanical, Radiation, Electrical, Work Environment and Work Activities Hazards. The risk assessment checklist includes details safe condition and working mechanism of Pumps, Instrumentation, Pressure vessel, Storage tanks, Fired heaters, Exchangers, Emergency Response Program, Facility Layout/Sitting etc. P. 111