Vertical seismic resolution quantifies the ability to distinguish between two close seismic events generated at different depths. A typical seismic dataset with a dominant frequency of 30 Hz allows the separation of top and base boundaries of a 25-meter thick reservoir layer. However, very often hydrocarbon bearing reservoirs are significantly thinner and, therefore, the vertical seismic resolution has to be increased in order to image and characterize those thin reservoirs properly.
The present study illustrates the application of spectral inversion technique based on high-resolution spectral decomposition offered by Lumina Geophysical, LLC. Spectral inversion can be described as a sparse-spike inversion driven by geological assumptions. It keys on local frequency spectrum obtained by spectral decomposition. Theoretically, a high signal-to-noise ratio and the exact knowledge of the seismic wavelet at reservoir level yield seismic resolution far below tuning thickness.
OMV chose to apply spectral inversion to various datasets recorded in Kazakhstan, West of Shetland and in Austria, covering different geological settings (e.g. channel features, sub-seismic faulting). Furthermore, a synthetic dataset has been designed and examined to illustrate benefits and pitfalls of the methodology. Each recorded seismic dataset showed significantly improved vertical seismic resolution after applying spectral inversion. The spectral inversion result for the marine seismic dataset (West of Shetland) showed increased seismic resolution and superior fault imaging compared to the conventional seismic data. Furthermore, seismic-to-well ties - including a blind well - very well support the realistic increase in vertical seismic resolution of the Kazakhstan seismic dataset. Finally, the evaluation of the onshore seismic dataset in Austria facilitated a new interpretation of the target sands which resulted in a revised geological model.
After careful evaluation of spectral inversion, OMV is convinced that this technology offers a valuable approach for better delineation and characterization of thin reservoirs and further projects will be performed.
Acharya, Mihir Narayan (Kuwait Oil Company) | Kabir, Mir Md Rezaul (Kuwait Oil Company) | Al-Ajmi, Saad Abdulrahman Hassan (Kuwait Oil Company) | Pradhan, San Prasad (Kuwait Oil Company) | Dashti, Qasem M. (Kuwait Oil Company) | Al-anzi, Ealian H.D. (Kuwait Oil Company) | Chakravorty, Sandeep (Schlumberger)
The deep, sub-salt reservoir complex is tiered with fractured tight carbonate at bottom and top, with the two sub-units of "upper unconventional kerogen?? and "lower inter-bedded kerogen-carbonate?? in the middle. This depositional setting is challenging for horizontal well placement where the thicknesses of respective sub-units are about 50 and 30 feet with varying geomechanical and petrophysical properties. Additionally, this complexity poses limitations in completions and effective stimulation of the Kimmeridgian-Oxfordian reservoirs in several gas fields at development stage in Kuwait.
A horizontal well is placed in the lower sub-unit of the laminated complex of unconventional kerogen and fractured carbonate reservoir as a Maximum Reservoir Contact (MRC) type well. A pilot mother-bore was drilled and logged to identify the lithological properties across the entire vertical domain - facilitates the optimization of horizontal drain-hole placement within the targeted reservoir units.
No wellbore stability issues in drilling were predicted based on the geomechanical understanding where core-calibrated logs from offset vertical wells were considered. However, this modeling method did not have the functionality to integrate the impact of drawdown on the laminated formation which became unstable and collapsed during the short open-hole drill-stem test (DST) plugging the tubing prior to the final completions. An alternative "book-shelf?? geomechanical model was considered at pre-drill stage for predicting the wellbore stability. Once the drilling was completed, the time-lapsed multi-arm caliper indicated the validity of the alternative methodology in predicting the unstable stack of laminations in kerogen-rich strata.
The paper discusses an optimization methodology to enhance the understanding of static and dynamic geomechanical stability through the use of BHI data. Objective of the proposed method is to help improve the effectiveness of completions where wellbore stability due to geomechanical complexity in stacked-pay reservoirs is a primary wellbore challenge in deploying the completions and executing a subsequent stimulation and testing campaign.
‘Safety First,' the motto of petroleum industry has been in focus since early 20th century evolving HSE considerably and as of today, we have industry best HSE practices nevertheless accidents still happen. A welder lost his life after he entered inside a 30?? pipe to inspect a weld joint. This is despite safety alert being widely circulated two weeks prior for a similar accident happened elsewhere. Are accidents inevitable or preventable?
‘Preventable,' would be the intuit answer but when prodded deeply with a psychological perspective the scenario apparently leaves an ounce of doubt, ‘was it inevitable?' To demystify the fatalistic thinking, a psychoanalyst's perspective is required to unveil the latent human factors that lead to unsafe acts. Even the safety regulations cannot rein human decision making processes which are affected by cognitive biases such as intuition, overconfidence, illusion of control, confirmation, complacence and hindsight. Under such constraints, it is no surprise that incidents reoccur whereas companies search for compliance gaps in HSE implementation.
Taking into account the case study of fatal welder accident, this papers explores human error and its influence on performance level, unveils human brain functioning, describe briefly five cognitive biases that influences unsafe acts, conjure the fatal welder accident with plausible biases, and concludes calling for more efforts to increase the awareness of cognitive biases and develop a safety culture helping to prevent incidents and improve HSE performances.
Key words: HSE, human error, performance, cognitive biases, metacognition, safety culture.
A project study has been performed in order to evaluate a number of reservoir characterization and petrophysical parameters using Digital Rock Physics (DRP) technology in complex carbonate reservoir, on-shore Abu Dhabi. High-resolution images (X-ray micro-tomographic) of the rock's pores and mineral grains were obtained, processed and the rock properties were evaluated by numerical simulation of the physical processes of interest at the pore scale.
The selection of core samples in carbonate reservoir was performed with considering reservoir rock type, logs and routine core analysis data for validation and application phase. A set of special core analysis (SCAL) data were acquired earlier on the core samples in different carbonate reservoir rock types of varying levels of heterogeneity, lithology, porosity, and absolute permeability. This set of measurements formed the baseline for our validation study, then similar DRP approach and improvement is applied for non-SCAL cores. This process is used in DRP study to evaluate cementation exponents ‘m', saturation exponents ‘n', water-oil relative permeabilities, capillary pressures and elastic parameters such as compressional/shear wave velocities.
An integration of core and logs data in particular carbonate reservoir has been used to provide accurate and reliable results in the validation phase of DRP. It has been observed in DRP that connected micrite phase conductivity contribution has been determined for improvement approach by assigning a finite conductivity smic to the micrite phase to get reliable formation factor, cementation and saturation exponent. DRP and core J-capillary were integrated to provide reliable saturation-heights in this carbonate reservoir. The integration of formation evaluation in this case study has provided improvement, reliability in DRP results for formation evaluation and the potential to improve the quality and timeliness of carbonate reservoir characterization.
The importance of maintenance in the oil and gas industry is well recognized and as such every year great sums are spent on reducing turnaround and mean time between failures while all the more increasing equipment availability and achieving acceptable levels of work force certification. ADMA-OPCO as one of the world's largest companies in the upstream sector of the oil and gas industry has managed to utilize various available technologies to achieve high standards of maintenance. However, the field of engineering maintenance and reliability is an ever evolving one and due to many factors such as aging machinery and the expansion of operations, the company's underpinning maintenance practices and strategies require constant review and update. For this purpose the paper will present a review of the company's achievements in this regard as well as outlining solutions for future challenges. The findings will be based on scrutinizing current practices such as the utilization levels of the computerized maintenance systems in use in ADMA. Moreover, this paper will endeavour into finding out how well the company's maintenance strategy is adhered to and the major constraints that hinder its smooth execution. Age of the rotating equipment plays an important factor in the levels of maintenance they require; therefore this paper outlines the effect this has on the maintenance strategy and the likely future consequence of this factor taking into account the challenges ahead.
Keywords: Reliability Centred Maintenance, Bathtub Curve, Failure Mode Analysis and Organisational Restructuring.
A narrative on injection of CO2 for enhanced oil recovery considering the advantages of the integrally geared compressor over the single shaft compressor, and using the Siemens hermetically sealed canned motor-compressor in the process of separating export gas and CO2 for reinjection.
When injecting CO2 for EOR we have investigated the most important market requirements to identify the best solution from the existing portfolio of turbo machinery, when comparing a standard single shaft inline compressor to an integrally geared compressor, and have concluded, based on economics, efficiency, and power consumption, that integrally geared turbo compressors incorporate the optimum design concept for economic CO2 compression.
When re-injecting the produced gas after oil and gas separation there is a mix of saturated CO2 and hydrocarbons and other contaminants possibly containing hydrates, mercury and H2S. Gases and components which are preferably contained in the process equipment without possible leakages to the atmosphere due to seal leakages or malfunction of the compressor units dry gas seals. With the above in mind we developed a sealless (no dry gas seals) compressor which could add strategic benefits and eliminate the need for continuous flaring and venting of the seal gas and barrier gas to the atmosphere. And in conjunction with a fully categorized material selection provide the best solution with high availability and reliability.
Combined with the increased robustness of the overall system with less instrumentation and auxiliary systems and thus less spurious trips and downtime it is obvious that the integrally geared turbo compressor, STC-GV, in combination with the hermetically sealed compressor, STC-ECO, has the potential to considerably contribute to minimizing the environmental foot print, higher reliability and lower OPEX in the Oil & Gas operations especially in the process of mixed flow dirty gas separation found in the CO2 reinjection application.
This paper summarizes 10 years of experiences on pumping cement through bottomhole drilling assemblies - BHAs. Despite a lot of industrial skepticism, a total of 79 cement jobs have been performed through a variety of drilling assemblies, in 3 categories of job types:
i) Curing critical mud losses to restore well control
ii) Plugging back pilot holes
iii) Planned plug or squeeze jobs
The job objectives were met for all the cement jobs performed, and high risk well control situations were resolved. The cementing operations have been performed from different types of offshore installations, like fixed platforms, semi-submersible rigs, as well as from TLP's - Tension Leg Platforms.
Most significantly, critical mud losses have been cured by pumping totally 13 cement jobs through rotary steerable drilling assemblies. Losses were cured and well control restored by performing jobs mainly through 8 ½?? - and 12 ¼?? drilling assemblies. The most severe case handled HPHT conditions and cesium formate drilling fluid.
By taking a controlled risk, the total well risk is significantly reduced. Time and huge costs are saved by performing cement jobs that are instinctively considered as a threat to well control. By planning these cement jobs carefully, the total risk of performing the operation through the bottom hole assembly is reduced.
After gaining experience from some severe, un-planned lost circulation incidents, a best practice was developed and implemented in order to be better prepared, especially for the un-planned events. The same procedures have also been implemented in the planning phase of drilling operations and some cementing operations are planned and executed this way.
Compositional heterogeneities of H2S have been noticed in many sour gas reservoirs. Its occurrence is an important factor of economic depreciation. Thus, the knowledge of its content and distribution is a critical parameter when planning field development. The paper aims at exploring the role of an active aquifer in the creation of H2S heterogeneities in high H2S-bearing gas reservoir. Indeed, under conditions of pressure and temperature of typical reservoirs, H2S is far more soluble than hydrocarbons and other gases. A preferential leaching of H2S (e.g. versus CH4) over time is thus possible.
This mechanism is controlled by: (1) Differential solubility of gases, which change the relative amounts of each gas near the gas-water contact (GWC); (2) Contact with an active aquifer, which can export the dissolved gases thus enhancing dissolution on the long-term; (3) Diffusional transport in the gas phase, which transfers the compositional anomalies farther from the gas-water contact; (4) Geological parameters (type of aquifer, permeability heterogeneities) which can modify the transport scenario.
To illustrate and quantify this process, we show the results of numerical simulations, performed with the two-phase transport and geochemical software Hytec. First, a very schematic reservoir with a composition considered uniformly distributed within the reservoir, has been simulated to quantify the leaching of H2S. The results highlight the potential role of the active aquifer, which can leach the gases and export them outside the reservoir. In a second phase, the effect of geological parameters on the H2S heterogeneity development was studied: additional simulations were performed on geometries closer to natural cases. The amount of leached H2S depends strongly on the geometry: the larger the GWC area, the larger the amounts leached.
Tursinbayeva, Damira (Tengizchevroil) | Lindsell, Karl Michael (Tengizchevroil) | Zalan, Thomas Anthony (Tengizchevroil) | Dunger, Darrin Allen (Chevron Corporation) | Kassenov, Baurzhan (University of Tulsa) | Howery, Randy (Tengizchevroil)
Over the field life, surveillance in Tengiz oil field has provided historical and baseline data for simulation history matching, static and dynamic reservoir characterization and modeling, and the foundation for efficient well management. Hence, it continues to be an important part of everyday field operations. At the surveillance planning stage, the comprehensive opportunity list of well candidates is developed based on input provided by members of multiple teams: geologists and petrophysists, production and reservoir engineers, drilling and field operations specialists. SCADA system, permanent downhole gauges (PDHGs) and multiphase flow meters (MPFMs) are widely implemented for production data acquisition and analysis. However, the majority of surveillance activities still need well intervention into the high pressure, high H2S concentration wellbores, often during harsh weather conditions. Each job execution plan is therefore focused on the safest procedure to obtain the necessary data. Each planned survey in the surveillance plan is ranked according to the value of information to be obtained, in order to help schedule the timing of surveillance based on plant production needs.
The ultimate goal is to safely execute planned surveillance to support production optimization and field development work. This paper will highlight TCO success in addressing the different reservoir and well production uncertainties through a properly designed surveillance plan with both short and long-term objectives.
Transient linear flow diagnostic plots in shale gas wells often exhibit a positive y-intercept and may mask the early transient linear flow regimes because of non-reservoir pressure drops. Increased completion resistance reduces the peak production rate early in the life of a well impacting NPV. The shale gas industry is very early in the research required to distinguish the individual contributions of completion resistance, e.g. poor fracture conductivity, near-perforation damage or choke skin, and fracture face damage skin. Many of these phenomena can be diagnosed in production wells using unique shape(s) from various diagnostic plots allowing for analysis of completion effectiveness.
Mechanistic reservoir simulations were used to generate diagnostic plot signatures for low conductivity fractures, choke skin, and near fracture face damage. Subsequently, the corresponding signatures were compared with a large database of shale gas wells in numerous plays across North America to aid in the fingerprinting of these non-reservoir pressure losses. Only low fracture conductivity, not choke skin, can have a quarter slope. Near fracture face damage results in two distinguishable linear trends, one of the damaged region and the other for the matrix.
Completion skin diagnosis is a way of evaluating fracture efficiency by identifying the root causes of the non-reservoir pressure losses so as to mitigate them in the future. The following presents a catalogue of signatures that enables greater diagnostic capabilities to classify non-reservoir pressure losses. The study is the first comprehensive cause-by-cause look at completion damages with an emphasis on identification and diagnosis in shale gas wells.