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Lagos, Nigeria

Ugochukwu O.,Addax Petroleum | Verity S.,Paradigm
38th Nigeria Annual International Conference and Exhibition, NAICE 2014 - Africa's Energy Corridor: Opportunities for Oil and Gas Value Maximization Through Integration and Global Approach | Year: 2014

The quest to appraise un-stacked reservoir sands and other surface location constraints has given rise to complex wellbore profiles due to the requirement of building angles and azimuth changes through these targets. This has increased the length and inclination of the wells drilled in the past decades. There are also larger departures and more tortuous wellbore. These trajectories can give rise to excessive torque and drag during the well delivery. Excessive drill string torque and drag is one of the major limitations of horizontal and extended reach wells, and when unplanned is a primary limiter. Because of the increased costs and risks in these wells, torque and drag analyses is recognized as an important part of the risk management process. Torque and drag models have proven to be very useful in the planning, drilling and post analysis of these difficult wells. During the planning stage they are used to optimize the trajectory design to minimize the torque, drag and contact forces between the drill string and the borehole wall. They are used during operations to monitor the hole conditions while drilling, diagnosing hole cleaning problems, watching out for impending differential sticking, and monitoring for high torque in planned highly tortuous trajectories. In post analysis the models help to determine the true causes of the hole problems, which will further be highlighted, documented and used to optimize operations. Accurate torque and drag analysis gives an opportunity to build reliable well trajectories, as it will take into account the capabilities of the rig and the geological complexity of the formation to be traversed. Ideally the model must be able to predict with minimal error the forces and along the wellbore. Generally the discrepancy between torque and drag prediction and actual measurements in conventional wells is within 20% depending on the variables used. This percentage error might increase or decrease depending on the variables used for these models. In this paper, a general overview of the torque and drag model is presented. It is then discussed how the Paradigm Sysdrill software has been able to accurately predict the torque and drag values of a planned wellbore. The error margin between the predicted and actual values was very minimal. This software has been able to effectively aid in the planning, monitoring and helped to give a reasonable and concise post mortem of the subject well that will be used as the case study in this paper. Copyright © (2014) by the Society of Petroleum Engineers All rights reserved.

Nwagu C.,Addax Petroleum
Society of Petroleum Engineers - SPE Nigeria Annual International Conference and Exhibition, NAICE 2015 | Year: 2015

Addax Petroleum Nigeria operates the OML-126 and 137 blocks in Nigeria. These are adjacent oil and gas blocks, located in the Niger-Delta region offshore. The close proximity of these blocks, and their similarity in terms of reservoir formation, means drilling activities in these blocks have had similar experiences. Past exploration wells targeting deep reservoirs in the blocks have experienced well control incidents resulting in the loss of millions of dollars due to the loss of several Bottom Hole Assemblies (BHAs), the loss of the wellbores and consequentially the premature termination of the projects. These well control issues were largely due to the pore pressure uncertainties in these blocks, which made it difficult to determine and plan the appropiate mud weights, required for the high pressures of the deep reservoirs. The Star-6 (ST-6) well was a subsea High Pressure High Temperature (HPHT) exploration well, which was successfully drilled by Addax Petroleum Nigeria between September - October, 2014. The well is located in the OML-126 block. Despite the short time frame for planning the well, with a range of possible pressures and temperatures, the drilling and exploration teams worked together to maintain safety and performance, and to overcome various logistical and operational challenges. The success of the well can largely be attributed to; the detailed well engineering planning, successful implementation of lessons learned from past exploration drilling activities in the area and utilization of industry recommended drilling practices. This case study, takes a look at the different stages of well planning and actual execution of the ST-6 well that led to the drilling by Addax Petroleum Nigeria, of the first successful exploration well to date that met all its objectives in the OML-126 block. Copyright 2015, Society of Petroleum Engineers.

Ugochukwu O.,Addax Petroleum
Society of Petroleum Engineers - SPE Nigeria Annual International Conference and Exhibition, NAICE 2015 | Year: 2015

Hydraulic modelling is an integral part of drilling operations, thus its importance for the efficient delivery of a wellbore cannot be over emphasized. The standard API methods for drilling fluid hydraulics assume either Power law or Bingham Plastic, these models provide a simple way of estimating required parameters for efficient drilling operations, but for conventional wells. These models are sometimes not accurate when used to model the hydraulics of more difficult wells. When drilling fluid is circulated, pressure drop takes place due to friction between the fluid and the surface of the stand-pipe, rotary hose, swivel, Kelly, drill-pipe, drill-collar, drill-bit, and the annulus between the drill-string and the open hole or casing. This generates a total frictional pressure drop in the hydraulic circuit called the Stand Pipe Pressure (SPP). The Equivalent Circulating density (ECD), which is generated from annular pressure losses, needs to be predicted correctly to ensure that the fracture gradient of the formation to be drilled is not exceeded, as there will be losses of the drilling fluid into the formation and potential wellbore instability problems. The paper discusses seven (7) rheological correlations/equations from studies (Robertson-Stiff, Casson, Carreau, Sisko & Willamson, Hershel Buckley, Cross and Modified Bingham Plastic) which have been used in different conditions to simulate and predict the parameters required for efficient hole cleaning operations. It then highlights the magnitude of failure that occurs when simple hydraulic correlations/ models are used for complex wells and very viscoplastic fluids. The paper compares and discusses the variation with actual results when the Bingham Plastic, Power, Hershel Buckley and Robertson Stiff models are used to model fluid hydraulics. It proposes that the correct hydraulics of a particular well depends on the nature of the reservoir and bottomhole conditions, as the data from an offset well might not be representative of a target well. Thus it is required that an engineer should run different simulations using different hydraulic models and then compare with the actual data during operations. The difference between the simulated and actual can be used as the fudge factor to further optimize the hydraulics for other hole sections or wells with similar configurations, if the best fit hydraulic model is unavailable in the simulator. Copyright 2015, Society of Petroleum Engineers.

Okoli U.,Addax Petroleum
Society of Petroleum Engineers - 37th Nigeria Annual Int. Conf. and Exhibition, NAICE 2013 - To Grow Africa's Oil and Gas Production: Required Policy, Funding, Technol., Techniques and Capabilities | Year: 2013

The cost of drill bits represents only approximately 3-4% of the authorization for expenditure (AFE) of well construction, but by their overall performance, affect 15-20% of the overall well cost which can either be positive due to increased rate of penetration (ROP) or negative due to trouble time (TT) losses due to the wellbore or invisible lost time (ILT) due to connection times or other failures. When these costs are considered, the selection of the appropriate bit can be seen to be key of the overall economics of field development. Bit performance represents the achievement of preset objectives which include revolutions per minute (RPM), weight on bit (WOB) and flowrate-hydraulics inclusive. These are a function of the rate of penetration (ROP), footage, and dull grading in a given formation. Bit behavior represents the ability to achieve the required directional control within the confines of a systemized drilling environment. It is a function of the bottom hole assembly, the planned tortuosity of the well (well directional profile) and the operational environment. In a new development, the typical procedure for the selection of drill bits is for the operator to initially approach drill bit vendors with a data package which contains information (lithology, log information(sonic, density-neutron), and bits graded from offset wells, these are used for the proposed wells as offset information. Drill bit vendors then put together a proposal based on this data and local experience; usually there is no way of validating the bit recommendation except by running the bit and evaluating the dull grade when out of hole, should the bit performance not meet the expectations then a new bit is tried. This method of trial and error exposes the operator and sometimes the cost impact is massive and has its effect on the project. The technical limit cycle is a conceptual feedback tool for maximizing drilling efficiency, and this paper presents how proper bit selection and proper hydraulics will help to increase the ROP of a well. This in turn helps to reduce all the trouble and invisible lost times which can be created by hole cleaning, high unplanned tortuosity, vibrations, helical/sinusoidal buckling of strings, bit whirls, excessive drags which distorts the planned time of drilling a well. This increases the well cost and increases the technical limit value of the well but the reverse when the right bit is chosen and flat times eliminated. Copyright 2013, Society of Petroleum Engineers.

Okoli U.,Addax Petroleum
Society of Petroleum Engineers - 37th Nigeria Annual Int. Conf. and Exhibition, NAICE 2013 - To Grow Africa's Oil and Gas Production: Required Policy, Funding, Technol., Techniques and Capabilities | Year: 2013

Reservoir estimation and evaluation during the exploration and appraisal phases of an Asset has proven very challenging due to the data uncertainties of the Reservoir. This makes the original oil in place calculations erroneous. Some of the Petrophysical data include the permeability, porosity, formation resistivity factor and saturation of water. The Porosity of the reservoir rocks and its permeability can be said to be the most fundamental physical properties with respect to the storage and transmission of fluids. These properties might also have an effect on the Formation resistivity factor, Saturation of water and then the whole Oil in place estimation. Thus, the accurate knowledge of these properties for any hydrocarbon Reservoir, along with the fluid properties is required for efficient development, management, and prediction of future performance of the oilfield Asset. This paper discusses the development (modelling, programming and simulating) of I-PETRO, a software designed to aid the evaluation of Petrophysical data, with reference to data from all the various Depobelts in the Niger-Delta. They incorporate all existing Models and correlations (Global and Regional), which thus allows the user to be able to compare the obtained value with existing correlations. It also helps to evaluate the oil in place. It was developed with Visual Basic 6.0. It is user friendly, reduces complexities in facies analysis, perform Petrophysical properties evaluation and is fully accompanied with an encompassing unit's converter. The first step of achieving the objectives of this project was to develop correlations for Formation Resistivity and Porosity especially for the Niger Delta from 156 data points, these points were taken from different regions of the Niger Delta Depobelts (Northern Delta, Greater Ughelli, Coastal Swamp, Central Swamp and the Offshore Depobelts) and they were compared with Global correlations. I-PETRO software was then developed using an algorithm, which was used to develop the program to estimate Petrophysical parameters and then the oil in place, taking into consideration all the required correlations required for more accurate evaluations. Copyright 2013, Society of Petroleum Engineers.

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