This paper presents the results of a study for estimation of reserves in a highly complex naturally fractured reservoir off the Coast of California. The fractured reservoir at the Point Arguello Field, consisting of the siliceous rocks of the Monterey Formation, has produced more than 187 million barrels of oil during the last three decades primarily from fractures intersecting the extended reach and directionally drilled wells. This study was conducted to assess the economic viability of continuing production of the field and economic incentives for maintaining operations at the three existing offshore production platforms. In our study we examined the remaining reserves from the fracture controlled production and scrutinized the potential contribution of the tight matrix to primary recovery and for EOR processes. In this integrated and comprehensive study, we used a new interpretation of 3D seismic data, re-visited extensive mud log data, prepared diagnostic plots of performance data and incorporated conventional logs, DST and core data to characterize the production system.
From the analysis of GOR, WOR, and 3D seismic we identified 10 separate compartments and related the vast differences observed in well productivities to the compartment size, degree of fracturing and behavior of water influx. We also developed common sense reservoir forecasting solutions to examine the potential application of CO2 injection for extracting oil from the tight matrix. The economic forecasting indicates substantial opportunities by managing water influx, exploiting bypassed intervals by new perforations, and drilling infill wells in blocks using volumetric curvature analysis data.
Lessons learned show the definitive significance of integrated reservoir characterization, importance of mud logs and 3D seismic, and fault characterization for defining compartments, and potential applications to other similarly fractured reservoirs.
Awe, S. O. (Shell Petroleum Development Company) | Usim, M. (Shell Petroleum Development Company) | Akinfolarin, A. (Shell Petroleum Development Company) | Erinle, A. (Shell Petroleum Development Company) | Ibrahim, T. (Shell Petroleum Development Company) | Roes, V. (Shell Petroleum Development Company)
Data from Measurement While Drilling (MWD) tools are critical to successful drilling operations, because they aid real time assessment of down-hole conditions and support critical decision-making. De-risking lithology and pore pressure uncertainties while drilling exploration wells are reliant on these measurements. The reliability of MWD tools is known to be affected by mud properties, such as concentration of low- and high-gravity solids, mud viscosity and gel strength. The high mud density required for deep well drilling operations requires an unavoidable increase in solids content, which can lead to tool failure if the fluid design or quality of constituents is suboptimal.
The upper part of the 8 ½" section of the BGG-S1 HPHT well was drilled with mud weight of 16 lb/gal. The mud weight was increased to 16.3 lb/gal because of the higher pore pressure prognosis across the deeper reservoirs. The increase in mud weight resulted into higher solids content as a result of addition of more weighting agent to the fluid. After the mud weight was increased, multiple BHA runs were made because the power module of the MWD tool was not responsive. Further investigation of the repeated failures identified the root cause as solids drop-out when flowing mud through the MWD tool. The poor quality of locally sourced barite used in the operation contributed to the poor performance of drilling fluid, because it resulted in higher solids content in the mud.
The solids deposition challenge was resolved by conditioning the mud to an emulsification specification that is higher than conventional industry practice. The well was eventually drilled successfully to TD after the treatment, using a single BHA run with continuous MWD data acquisition and transmission. This paper reports the impact on the mud system associated with the quality of barite, the failure mode of the MWD power module, and the treatment of the mud to ensure technical success of the drilling operations on BGG-S1.
Adesina, Fadairo (Department of Petroleum Engineering, Covenant University) | Paul, Anawe (Department of Petroleum Engineering, Covenant University) | Oyinkepreye, Orodu (Department of Petroleum Engineering, Covenant University) | Adebowale, Oladepo (Department of Petroleum Engineering, Covenant University)
Horizontal wells have become a popular alternative for the development of hydrocarbon fields around the world because of their high flow efficiency caused by a larger contact area made with the reservoir. Most of the analytical model existing in the literature on horizontal productivity either assumed that the well is infinitely conductive or the flow is uniform along the entire well length.
Amoyedo, Sunday (Total Upstream Nigeria Ltd.) | Atoyebi, Haraya (Total Upstream Nigeria Ltd.) | Bally, Joakim (Total Upstream Nigeria Ltd.) | Usman, Musa (Total Upstream Nigeria Ltd.) | Nateganov, Arthur (Total SA) | Bergamo, Laurent (Total SA) | Berthet, Philippe (Total SA)
Reservoir models often tend to be simple and do not always represent typical reservoir property variations and sometimes complex communication patterns typically encountered in deepwater turbiditic systems (amalgamated, laterally-offset stacked channel complexes and lobate systems). Consequently, such models prove unreliable for development planning and long term production forecast. To address this, seismic facies, which are derived from 3D inversion and subsequent classification studies, are often used either as a background trend or direct quantities in static model building process to guide both lateral and vertical reservoir grid population away from well control points.
In this paper, we discuss a methodology for the integration of well data (reference data) and seismic reservoir facies probabilities (auxiliary data) to build a seismic-consistent static reservoir model in a deep-water field, deep offshore Niger Delta. The methodology captures both vertical and lateral variations in reservoir quality seen on well logs (after up-scaling) and seismic-derived reservoir properties inferred from 3D and 4D seismic. Furthermore, we discuss the challenges (fault shallow effect, amplitude degradation across fluid contacts, etc.) and pitfalls (inversion uncertainties, clustering/classification uncertainties etc.) of seismic-driven reservoir facies modeling and their impacts on the reservoir history matching process. Additionally, we discuss potential corrective measures to address some of these challenges, thereby enhancing the consistency of seismically-derived reservoir facies.
The paper concludes with the validation of the geologic model with the use of 3D seismic loop-back process.
Enyekwe, Alfred (The Shell Petroleum Development Company Nigeria Limited.) | Urubusi, Osahon (The Shell Petroleum Development Company Nigeria Limited.) | Yekini, Raufu (The Shell Petroleum Development Company Nigeria Limited.) | Azoom, Iorkam (The Shell Petroleum Development Company Nigeria Limited.)
Significant emphasis on data quality is placed on real-time drilling data for the optimisation of drilling operations and on logging data for quality lithological and petro-physical description of a field. This is evidenced by huge sums spent on real time MWD/LWD tools, broadband services, wireline logging tools, etc.
However, a lot more needs to be done to harness quality data for future work-over and or abandonment operations where data being relied on is data that must have been entered decades ago and costs and time spent are critically linked to already known and certified information.
In some cases, data relied on has been migrated across different data management platforms, during which relevant data might have been lost, mis-interpreted or mis-placed. Another common cause of wrong data is improperly documented well intervention operations which have been done in such a short time, that there is no pressure to document the operation properly. This leads to confusion over simple issues such as what depth a plug was set, or what junk was left in hole.
The relative lack of emphasis on this type of data quality has led to high costs of work-over and abandonment operations. In some cases, process safety incidents have arisen.
This paper looks at some work-over operations carried out in a span of 10 years. Data management system is generally analysed and a categorisation of issues experienced during the work-over operations is outlined. Time lost due to data error was seen to average 1.54% but with a unit peak of 19%. An analysis is done on the wells' activity history to check for correlations. Bottlenecks in data management are defined and solutions currently being implemented to manage these problems are listed as recommended good practices.
In compliance with local regulation in Nigeria on open water discharge and environmental stewardship considerations, aqueous Gas-to-liquid (GTL) plant effluents usually treated to meet specification for discharge to the Escravos River were characterized for consistency in quality for disposal by injection into oil/gas reservoirs.
Gas-to-Liquid plant operated by Chevron in the Escravos area has considered the discharge of their aqueous effluent water through the Escravos Produced Water system as an alternative to river dump. These effluents are different in composition and quality with produced water from Oil/Gas reservoirs due to the various sources producing the effluent. To qualify for reservoir disposal, a detailed characterization of the GTL effluent was performed to determine acceptable potential impact on the surface and subsurface facilities.
This paper therefore provides the necessary technical evaluations required for effective reservoir disposal of GTL effluent water when considered to supplement the injection volume or serve as alternative injection water to the conventional produced water re-injection.
The geomechanical knowledge of rocks physical and mechanical properties could reduce the NPT incurred while drilling and production of a reservoir to a large extent by selection of proper/optimum operating envelope. Hence, a field development plan for each oil/gas field may contain optimized geomechanical procedures that take into accounts the rock mechanical principles and failure scenarios. "The unconfined compressive strength (UCS) and internal frictional interplays of rocks is the important rock mechanical parameters that plays crucial role when drilling an oil or gas wells". "(UCS) is the stress level at which rock is broken when it is under a uniaxial stress state (Bruce et al 2004)"; it can be used for real – time wellbore stability evaluation, bit selection management, and design of enhanced geomechanical earth models and cap integrity evaluation. Rock strength can be estimated along drilled wellbore using different approaches, including laboratory tests, core – log relationships and rate of penetration models. The benefit of a petrophysical log- derived method is that, it provides continuous strength profiles with depth. This is useful in delineating differences between near uniform zones, and identifying weaker zones. There is also a cost advantage in obtaining these data without having to perform extensive laboratory testing throughout the core interval.
"In this study, new equations for estimation of rock strength in Niger Delta formations are formulated based on empirically derived models that accommodate petrophysical log information such as the degree of shaliness detected over the entire logged interval, corresponding to shale and sand units (Fjaer, et al. 1990), lithology index etc., hence they are utilized for estimation of the rock strength profile for easy and effective geomechanical evaluations" (Dosunmu 2007).
A geomechanical enhanced framework coupled with discrete finite element analysis is utilized for prediction of UCS in any predefined well trajectory and batch depth analysis on the course of this research (study). Cross/post – validation shows that, the results from the formation discretization were compatible with realities (based on MEM utilization). This approach has proven to be useful for estimation of rock strengths and frictional interplays in any design well trajectory prior to drilling (predrill scenarios). Above all, it helps to determine the minimum and optimum mudweights required for real – time wellbore stability management during drilling, POOH, casing running and cementing, helps in preventing unplanned events leading to outrageous NPT's (Otutu 2013)
Reservoir fluid properties data are indispensable in reservoir engineering evaluations and computations. Ideally, those data should be obtained experimentally. On some occasions, these data are either not available or grossly unreliable; then, empirically derived correlations are used to predict PVT properties. Most correlations in the literature were either modelled using regional data or their level of accuracy is low.
Artificial neural network is a new computation strategy that could be used to generate model for predicting PVT properties. It consists of simple arrangement of nodes, called neurons, used for pattern recognition, modeled after a representation of human brain.
The author has explored the use of neural network in estimating bubblepoint pressure and formation volume factor at bubblepoint pressure with the aim of getting more accurate prediction compared to available correlations in the literature.
The number of data set used for bubblepoint pressure is 2114 and oil FVF at bubblepoint is 2024. Various neural network designs with one-hidden, two-hidden and three-hidden layers were considered and tested. The number of neurons in the hidden layer was varied until stable network was achieved. Each successful trained model was tested to ensure that overfitting does not occur and can predict output from inputs that were not seen by the model during training. Sixty percent of the data was used to train the network, twenty percent to cross-validate the relationships established during the training process and the remaining twenty percent to test the model.
The results of this study show that the model gives better prediction and higher accuracy compared to the published bubblepoint pressure and formation volume factor empirical correlations.
Asgharzadeh, Arash (Institute of Petroleum Engineering, Clausthal University of Technology) | Bello, Opeyemi (Institute of Petroleum Engineering, Clausthal University of Technology) | Perozo Baptista, Nelson Rafael (Institute of Petroleum Engineering, Clausthal University of Technology) | Paz Carvajal, Carlos Andres (Institute of Petroleum Engineering, Clausthal University of Technology) | Berdasco, Javier Holzmann (Institute of Petroleum Engineering, Clausthal University of Technology) | Oppelt, Joachim (Institute of Petroleum Engineering, Clausthal University of Technology)
The integrity of drill string while drilling especially under dynamic conditions plays a very crucial role in efficiency; reaching the target (pay zone) and even economical aspects. Considering the dynamics of drill string one would immediately think of vibrations; particularly torsional vibrations, posed on drill string. In worst cases the phenomenon of stick/slip occurs, in which the bit comes to a full stop and then accelerates uncontrollably. The non-uniform acceleration and deceleration of RPM continues to exist during drilling operation with possible catastrophic consequences. Bringing the bit off the bottom and adjusting the RPM are the conventional approaches which are performed on the surface.
This paper reviews and analyzes the present solution approach as related to drill string torsional prevention measures. Furthermore, a proactive solution would be proposed in contrary to the existing methods to prevent the occurrence of torsional vibration in both vertical and directional wells drilled with top-drive system, which will be performed downhole.
By rotating the drill string at top, it stores energy along itself. At a particular point in time drill string accelerates and rotates in an uncontrollable manner due to act of friction and spiral spring behavior of the drill string. During this process the stored potential energy in drill string is converted to kinetic energy.
The proposed approach entails the use of hydraulic power to prevent storing the potential energy along the drill string. That is, if there is an acceptable maximum level of stored potential energy, conversion into kinetic energy will not happen. By this means, the torsional vibrations are highly mitigated if not eliminated completely.
The proactive solution seeks prevention of a phenomenon (torsional vibrations) which can lead to calamities if not contained. However, efficient drilling and ROP are chief goals of drilling engineers. Also this proactive solution will be done down the hole not on the surface. Hence, more efficient drilling is sought by preventing one of most disastrous incidents.
Maduekwe, C. (World Bank Centre of Excellence for Oilfields Chemical Research, University of Port Harcourt) | Nwachukwu, E. O. (World Bank Centre of Excellence for Oilfields Chemical Research, University of Port Harcourt) | Joel, O. F. (World Bank Centre of Excellence for Oilfields Chemical Research, University of Port Harcourt)
The comparative study of RENA, Mycoremediation and combination of the two techniques were carried out to determine their ability in the degradation of selected heavy metals (Cadmium, Chromium, Nickel, lead, Zinc, Manganese and Iron) in a Crude oil impacted soil. Three different plots for each technique and control were each spiked with 7.5 Litres of Bonny Light crude Soil Samples were taken at 0-15cm and 15-30cm depths for each of the techniques and control at 0, 4, 8, 12, 16 and 20 weekly intervals for heavy metal analyses. Results indicated that in the plots treated with RENA, Mycoremediation and combination of the two techniques, Lead (Pb) concentration was degraded by 55.9%,65.8%,85.1% respectively compared with control plots that gave 23.7% reduction of Pb. The percentage degradation of Manganese by RENA, Mycoremediation and Myco/RENA was 57.3, 64.3, 83.1 respectively while control plots recorded 26.1% Mn degradation. Concentration of Ni was reduced by 57.8% by RENA, 64.2%, by Mycoremediation and 85.6% by the combination of the two techniques (Myco/RENA) while in the control plots Ni was reduced by 27.89%. Concentration of Cd was reduced by 56.7% 65.6%, 88.7% by RENA, Mycoremediation and Myco/RENA respectively. The control plots recorded 26.1% Cd degradation. This was similar trend observed for other heavy metals studied. Thus the combination of the two techniques (Myco/RENA technique) gave a promising result in the degradation of all the heavy metals studied in Crude Oil Impacted soil.