Khan, Riaz (ADNOC) | Al Hanaee, Ahmed (ADNOC) | Al Tameemi, Kate (ADNOC) | Kurniawan, Redy (ADNOC) | Omonigho, Neil (ADNOC) | Gueddoud, Abdelghani (ADNOC) | Abdelaal, Atef (ADNOC) | Vantala, Aurifullah (ADNOC)
The Gachsaran Formation across Onshore Abu Dhabi and possibly across U.A.E poses high potential of generating Shallow Biogenic Gas (mainly methane) and as such has taken the attention to further investigate, understand and evaluate its capability for promising Gas Resources. The paper provides a detailed G&G analysis that has potentially allowed an appropriate characterization of this unique formation that has first time uncovered interesting data responses in differentiating the sweet spot.
For the first time in the history of U.A.E., new data was acquired targeting specifically the Miocene, Gachsaran Formation. This includes; 2D Seismic and party 3D Seismic interpretations, thousands of feet continuous core, conventional and advanced subsurface and surface loggings, Formation Pressure, Fluid sampling, Geochemical and Geomechanical labs measurements, stimulations and Frac tests data. The Gachsaran Formation is very challenging due to complex, thinly bedded and intercalated lithological varitions, and tightness provides difficulties in identifying the promising areas of Gas bearing layers. A comprehensive analysis was performed, in the light of regional understanding, by integrating the results of all available data in the form of correlation, cluster analysis, cross plotting and well based rock physics to differentiate the effect of Gas existence within the formation. The potential zones were further tested and results were integrated to confirm the analysis.
The Gachsaran Formation has been subdivided into Lower, Middle and Upper Gachsaran Members. The Lower Member is predominantly evaporitic, becoming more argillaceous carbonate and shale –bearing in the the Middle Member with comparatively less anhydrites. The Upper Member contains mainly anhydrites with interbedded shales and carbonates. The potential sequences which represent high Total Organic Carbon and Gas Shows are found within the Middle Gachsaran.
Consequently, the Middle Gachsaran Member was analyzed based on the robust data acquisition performed. Several relationships among GR, TOC, Gas shows, Lithology, RHOB, NPHI, Sonic, AI, Vp/Vs, Gradient Impedance and XRD Clay mineralogy have been attempted to check possible identification of Gas existence effect on the data. This has led to identify the sweet spots caused by the existence of any dominant Gas within the Study Area. The potential zones were confirmed by well testing. Furthermore, data variables were distributed within a 3D Grid and based on the analysis performed the area of sweet spots were identified. In the next phase of the study, the results will be integrated with the upcoming Geophysical Seismic Inversion studies to further optimize the possibility of identifying the sweet spot across the Study Area.
The robust data acquisition targeting Gachsaran was performed first time in the history of U.A.E. The results are encouraging in establishing the relationship to identify the dominant existence of Gas effects within the area. The estimation of realistic Gas In-Place and its confirmation of commercial discovery will open a new era of Shallow Gas resources within U.A.E.
Increased demand for gas in the recent years has motivated Exploration companies to revisit erstwhile overlooked Miocene Biogenic gas potentials, onshore Abu Dhabi. This paper detail how advanced geophysics techniques including rock physics forward modeling and inversion has been integrated to understand the distribution of potential gas bearing zones in this complex unconventional setting where inter-well information is limited. The results integrated with understandings from other disciplines support drilling and field appraisal strategy in the area.
The Miocene Formation of interest consists of an Upper, Middle and Lower unit, with varying levels of complexities and hydrocarbon presence identified from drilled wells. We show how we integrated all available data including logs, core, fluids, cuttings, mud-gas, petrophysical and seismic information to constrain the seismic forward model and invert the seismic data to define potential for gas presence in the area. Lithologic boundaries were defined from cuttings and geologic correlations. Half-space rock properties analyses and well ties provided understanding of the seismic responses, and the geologic picks mapped accordingly. Gassmann fluid substitution were carried out using conditioned Vp, Vs and density logs to understand the sensitivity of the lithologies to different pore fluid fill including brine and different gas proportions. AVO forward modeling was also carried out to understand if gas ‘sweet spots’ may be visible from analyses of amplitudes. Rock physics plots were analysed including AI, SI, GI, PI and Lame's parameters to establish relationship to reservoir properties, and optimum discriminators of fluid, porosity and TOC were accordingly determined. The low frequency model was developed from logs, and prestack 2D seismic data up to 40° were inverted for elastic impedances. Bayesian rock type classification scheme was deployed to extract potential gas prolific areas.
Seismic rock properties analyses provided invaluable insight to the reservoir characterisation strategy for the Biogenic gas formation. The analyses showed that delineating gas presence is challenging using conventional amplitude or AVO analyses techniques. Potential for fluid optimization exists from analyses of poisson's impedance (PI) as well as extended elastic impedance at the fluid projection with reasonable certainty. Pre-stack simultaneous inversion of the seismic lines was carried out, followed by Bayesian rock type classification to identify regions of increased gas potential in areas of seismic coverage
This paper represents for the first time integrated seismic rock properties and inversion techniques are applied to delineate an unconventional Biogenic gas reservoir. The results hold potential benefit for well placement and input to distribution of reservoir properties in the geologic model. The method will be extended to analyzing the gas potential from the currently acquired mega 3D seismic over Abu Dhabi.
Taher, Ahmed (Abu Dhabi National Oil Company) | Al Hanaee, Ahmed (Abu Dhabi National Oil Company) | Frsnco, Bernardo (Abu Dhabi National Oil Company) | Chitrao, Amogh (Abu Dhabi National Oil Company) | Abdelaal, Atef (Abu Dhabi National Oil Company) | Popa, Desdemona (Abu Dhabi National Oil Company)
Recently there has been a growing interest in gas exploration, much of this focus has been directed toward thermogenic gas derived from cracking kerogen in the highly mature kitchens. However, a significant proportion of the global gas reserve is not thermogenic but of bacterial origin (
The recent exploration wells drilled in the northeast onshore Abu Dhabi showed elevated total gas readings during the drilling of the Gachsaran formation. Consequently, mud-weight was increased to control the gas flow. In addition, the recorded wireline logs indicate the presence of relatively high hydrocarbon saturations in several high porous zones of Gachsaran and Asmari formations.
To assess the productivity and commerciality of the Biogenic gas potential in Abu Dhabi, several exploration wells are planned to be drilled before the end of 2019. The positive results of these wells will open the door for a new era of sweet gas exploration activities in Abu Dhabi and its surrounding areas. The primary gas reservoirs are thin carbonate and clastics layers in the Gachsaran Formation at a depth that ranges between 1600-5200 feet below sea level.
Organic carbon isotopes, Rock Eval analysis, TOC log data and gas shows analysis indicated that the methane gas found in the Gachsaran Formation is of a biogenic origin and sourced mainly from the organic-rich argillaceous limestone of the Middle Gachsaran.
Gachsaran formation is comprised of alternating thin layers of anhydrite, limestone, marl and shale sediments in addition to the presence of salt layers in the lower part. This mixed lithology resulted in the reservoirs property deterioration in particular by shale and anhydrite nodules cementation.
The biogenic basin areal extent, significant thickness of the Gachsaran in this basin and the organic richness distribution, conclude possible generation of a huge volume of biogenic gas in northeast onshore Abu Dhabi. However, additional work is required to estimate the volume of gas that is accumulated and that can be produced from the Gachsaran and Asmari formations.
Deminova, Anna (Abu Dhabi National Oil Company) | Al Hanaee, Ahmed (Abu Dhabi National Oil Company) | Abdelaal, Atef (Abu Dhabi National Oil Company) | Vantala, Aurifullah (Abu Dhabi National Oil Company) | Aslanyan, Irina (TGT) | Abasher, Doha (TGT) | Skutin, Vasiliy (TGT) | Evdokimov, Stanislav (TGT)
Several shallow gas kicks in Miocene have been encountered during drilling in North East Abu Dhabi (Ghantoot area). Gas origin is confirmed to be predominantly biogenic. ADNOC is evaluating subsurface potential as part of its strategy in developing prospective shallow gas accumulation. Tight layers are targeted to unlock potentially high amount of hydrocarbons and to achieve economical production targets. This paper demonstrates effectiveness of a modern reservoir-oriented technique for well and reservoir performance monitoring before and after stimulation jobs. This technique was proved to be effective at exploration stage when cost- and production-effective stimulation methods are analyzed and decided upon.
The spectral acoustic logging technique was applied to estimate inflow intervals in the tight gas reservoir, including pre- and post-stimulation monitoring. Spectral acoustic sensors record signals in a wide frequency range from 8 Hz to 60 kHz. Their dynamic range of 90 dB and large scanning radius allow accurate recording of relatively low-amplitude reservoir acoustic signals. Comprehensive analysis of the spectral acoustic data in combination with other logging techniques, such as temperature logging and a heat exchange sensor (a type of heat flow-meter) can be potentially useful for verification of complex, low-permeability reservoir parameters.
Shallow tight Gachsaran and Asmari biogenic gas formations are currently under appraisal targeting identification of highly potential zones and screening of production enhancement technics that allow achieving economical gas rates. Different stimulation technics were evaluated while testing of several exploration wells. One of the way to evaluate stimulation efficiency is an integrated logging that includes high-precision temperature logging and broadband high-sensitivity acoustic logging.
Several logging campaigns were conducted in exploration wells to evaluate well performance before and after different types of stimulation jobs: routine HCl stimulation, advanced chemical stimulation, mini- and propped hydraulic fracturing.
Due to the reservoir tightness, matrix flow is extremely weak and doesn’t allow sustaining the flow with or without nitrogen lifting that exclude the possibility of routine production logging with spinners. Using of High Precision Temperature (HPT) and Spectral Noise Logging (SNL) allows production profile evaluation for tight reservoir when survey is conducted after series of nitrogen lifting.
Due to the complexity of reservoir mineralogy (presence of clays, gypsum, anhydrites) HCl routine matrix treatment is found to be inefficient. Due to the reservoir tightness and based on logging and testing results, it was concluded that any types of matrix stimulation would not be efficient production enhancement technic for biogenic gas tight formations. Propped hydraulic fracturing allowed to bring gas to surface in the vertical well; sustainability of the flow needs to be evaluated in the horizontal well with propped stage fracking.
Differentiation between matrix and fracture flow was possible while interpreting noise amplitude and frequency; conducting HPT-SNL logging after propped hydraulic fracturing allows identification the direction of fracture propagation and level of containment within the target interval. HPT-SNL logging was proved to be effective at exploration stage when cost- and production-effective stimulation methods are analyzed and decided upon.
In tight gas reservoirs with high heterogeneity and mineralogy variation, it is challengeable to select proper enhancement technic allows achieving economical production rates. Selected logging techniques allowed identification of low rate flow intervals in tight gas reservoir and evaluation the efficiency of different stimulation techniques.
This seminar will teach participants how to identify, evaluate, and quantify risk and uncertainty in everyday oil and gas economic situations. It reviews the development of pragmatic tools, methods, and understandings for professionals that are applicable to companies of all sizes. The seminar also briefly reviews statistics, the relationship between risk and return, and hedging and future markets. Strategic thinking and planning are key elements in an organisation’s journey to maximise value to shareholders, customers, and employees. Through this workshop, attendees will go through the different processes involved in strategic planning including the elements of organisational SWOT, business scenario and options development, elaboration of strategic options and communication to stakeholders.
Decisions in E&P ventures are affected by Bias, Blindness, and Illusions (BBI) which permeate our analyses, interpretations and decisions. This one-day course examines the influence of these cognitive pitfalls and presents techniques that can be used to mitigate their impact. Bias refers to errors in thinking whereby interpretations and judgments are drawn in an illogical fashion. Blindness is the condition where we fail to see an unexpected event in plain sight. Illusions refer to misleading beliefs based on a false impression of reality.
This paper presents a case of cluster well development in swamp wetland in high pressure salt gypsum formation of N.A Oilfield of Iran and analyzes the advantages and challenges of cluster drilling and completion. Experience and lessons learned from cluster drilling and completion are issued.
The major challenges of cluster drilling and completion is anti-collision and higher torque and drag in three dimensional trajectory well. The cluster drilling and completion is more difficult due to the existence of high pressure salt gypsum with high pressure salt water in N.A Oilfield. This paper presents well trajectory optimization design, anti-collision design and technical treatment to decrease drag and torque in three dimensional trajectory well for cluster wells in N.A Oilfield. The above mentioned cluster drilling technology has been used in more than 50 wells in N.A Oilfield and solve the three dimensional trajectory well drilling and completion difficulties such as drill string stuck, casing stuck and so on.
The key technology of the cluster well is trajectory design and control to drill a smooth hole and decrease collision. The completed wells show that the duration of three dimensional trajectory well is 10 days longer than that of the two dimensional trajectory well for 3D trajectory is more difficult for drilling, running casing, completion, acidizing due to higher torque and drag. So the composite cost of the three dimensional trajectory well is 1 million dollars more than that of the two dimensional trajectory well. It is economically feasible to use three dimensional cluster well for the cost of construction of one pad is about 3-4 million dollars in the swamp wetland surface conditions. The technical difficulties and economic evaluation shall be considered in the design of cluster well development and not all the cluster well drilling is economically feasible.
Cluster well is a practical and economic development mode in offshore oil production, offshore oil on the land and some harsh surface conditions such as swamp. Considering the complexity and cost of drilling three dimensional trajectory well, it is recommended to design two dimensional trajectory well in cluster well deployment if there is no limitation in the land surface condition.
Ibeh, S. U (Shell Professorial Chair, Federal University of Technology) | Chibueze, S. E (Shell Professorial Chair, Federal University of Technology) | Abonyi, C. L (Shell Professorial Chair, Federal University of Technology)
The value and contribution of natural gas in both domestic and economic terrains are extensive. However, its contaminants limits direct application and hence must be treated. Water vapour existing in equilibrium with dry gas is the principal among contaminants. Most corrosion both with acid gases and carbonate salts are traceable to the presence of water. Also the formation of solid icy structures called hydrates constitutes a threat to flow assurance. Removal of water by TEG dehydration trains is not uncommon.
Dehydration inefficiencies such as high water content of the outlet gas and glycol losses could impair operations and considerably reduce profit. Inefficiency in GDU was identified to be due to design factors and operational conditions/scenarios. In the case studied, laboratory analysis of TEG was combined with process simulation results to resolve inconsistencies in design and operational phases. Recommendations for further improvements were also presented.
The Cretaceous-aged reservoirs of Iran and their counterparts on the Arabian platform are among the most important carbonate reservoirs developed under the warm equable climate. Intense tectonic activities combined with the eustatic sea-level changes caused sporadic exposures of these carbonate successions in SW Iran and some other areas of the Middle East.
Under the domination of warm and humid climate and long-term exposures, several erosional disconformities formed throughout these successions. To investigate these palaeoexposure surfaces, petrographic and geochemical studies were carried out in four subsurface sections of giant and supergiant oilfields located in northern and southern parts of the Dezful Embayment.
Some of the most important diagenetic features (such as extensive meteoric dissolution/karstification, palaeosol development, and collapsed-dissolution brecciation) were used as evidence for recognition of main palaeoexposure surfaces and associated karsts.
Isotopic composition (δ13C and δ18O) and trace element concentrations of these carbonate rocks were used to elaborate the effects of these surfaces on diagenetic evolutions of palaeo-karstic Bangestan reservoirs. Both carbon and oxygen isotope ratios show a spectacular decline just below these disconformities in comparison with the expected values for the simultaneous marine carbonates, indicating that the Bangestan carbonates underwent extensive meteoric diagenesis. Elemental concentrations (Mn, Fe, and Sr) also point to moderate to intense meteoric diagenetic alterations associated with the palaeoexposure surfaces.
Palaeoexposures have had an irrefutable role in the formation of carbonate reservoir rocks under warm equable conditions (Weidlich, 2010; Mazzullo, 2004). These reservoir rocks ?namely palaeo-karstic carbonates? host an important portion (20 to 30%) of the world's hydrocarbon (Mazzullo and Chilingarian, 1992; Mazzullo, 2004). Owing to the influences of palaeoexposure surfaces on the reservoir quality of carbonates, they must be traced through rock record by considerable changes in facies characteristics, diagenetic features, paleontological evidence, and of the most importance, geochemical tracers (Immenhauser et al., 2000; Weissert et al., 2008).
Abiogenic and most of biogenic carbonate sediments precipitate geochemically in equilibrium with their contemporaneous sea waters (Veizer et al., 1999). Carbon and oxygen isotope compositions change through carbonate alterations. Ancient and modern exposure surfaces indicate a clumped variation in oxygen and carbon isotope compositions. Weight of eo-diagenetic alteration on the isotopic composition of carbonates is mainly controlled by several factors including soil-gas CO2, primary mineralogy and geochemical composition, meteoric waters characteristics, exposure duration, and system openness (Hudson, 1977; Allan and Matthews, 1982).
A large number of casing collapse reports is available in a big carbonate oil field in Iran (Gachsaran cap rock formation) which contains salt layers. In the majority of such problems, time is one of the key parameters. This has necessitated evaluation of time-dependent and rheological characteristics of salt layer of this Formation. To identify the rheological parameters of Gachsaran Formation, uniaxial creep tests at three different temperatures (23 to 100 Centigrade) are carried out, from which the creep curves as well as exponential functions of strain rate during the steady creep stage and creep constitutive equations of rock salt are obtained. Creep function for the rheological model is also presented in this study. The study results show that: (i) the creep constitutive equations of rock salt at different temperatures are in good agreement with the Burgers and generalized Kelvin models, besides which the respective characteristics of these two creep models are compared. (ii) Moreover, instantaneous strain is brought higher on the vertical axis of strain-time graph when temperature rises. In addition, the more temperature increases, the more steady creep is obtained. The results can provide some reference for long-term analysis of wellbore stability and cap rock integrity in Gachsaran Formation.
It is well known that some rocks possess viscoelasticity to some extent and exhibit time-dependent behavior during deformation (Chen et al 2006b). In particular, evaporative formations, such as Gachsaran formation where salt rocks are the major constituent, are known for their viscoelastic behavior accounting for responsible for the majority of casing collapses and cap rock integrity challenges occurred in almost entire Iran’s oil fields. Rheological characteristics of salts are considerably important since aforementioned formation accounts for most cap rocks of carbonate reservoir in Iran. In more recent times, numerous studies have been driven by the need to develop improved design and performance predictions for nuclear waste disposal and oil and gas storage (Chen et al. 2006b, Jin & Cristescu 1998).