Troudi, Habib (OMV Tunesien Production GmbH) | Chevalier, Francis (OMV Tunesien Production GmbH) | Alouani, Wael (OMV Tunesien Production GmbH) | Mzoughi, Wala (OMV Tunesien Production GmbH) | Abdelkader, Omri (OMV Tunesien Production GmbH)
In Tunisian Ghadames sag basin, a significant portion of natural gas resources are looked within low permeability Ordovician sandstones deposited immediately below the Early Silurian Tannezuft world-class source rock.
The objective of this study was to develop an integrated approach to better estimate the amount of gas stored in this emerging play via the analysis of four fundamental elements: 1) the thermal maturity of the Silurian ‘hot shales’ source rock, 2) the trapping mechanism and the architecture of Upper Ordovician paleo-valleys, 3) the impact of diagenesis-lithofacies association on petrophysical properties, and 4) the fracture distribution/density and their contribution in the production.
The Early Silurian hot shales constitute the essential ingredient for the development of a pervasive gas accumulation play. The gas generated at the deeper part of the basin has charged the underlying Ordovician low-permeability sandstones mainly through complex faults system inherited from the basement. During hydrocarbon maturation and charging, pore pressure increases at rates that exceed the normal gradients, leading to local over-pressure as seen in several wells drilled down to the Ordovician reservoirs. Lateral migration via regional faults is confirmed by numerous discoveries at the edges of the basin far away from the gas kitchen.
Besides the structural closures accumulations, more complex structural/stratigraphic or purely stratigraphic traps are deemed within the Late Ordovician, and documented for instance by the development of incised paleovalleys filled with multiple fluvio-glacial and marine clastic sediments (i.e Algeria, Libya). The discovery of hydrocarbon pay zones outside of structural closures and the result of the long term tests confirm this hypothesis.
Based on seismic data it is generally very hard to recognize the paleorelief marking the base of the Late Ordovician sequence. Key elements from core studies, regional correlations, isochore maps and sequence stratigraphy have been combined accordingly, leading to a conceptual model within the observed framework. It is then possible to identify the multiple incision surfaces associated with reservoirs of Jeffara and M'Krata Formations.
The reservoir quality is considered as a major risk in deep areas (>4 km). Although, the primary pores space have been occluded by quartz overgrowths and clay cementation or lost by lithostatic compaction. The substantial gas rates observed in several wells drilled in the junction of NE-SW and NS fault trends constitute an evidence of the contribution of open fracture into the flow.
This new insight into this play has been used by OMV to identify in Ghadames basin the area with possible "Tunnel Valley features", analogues to those drilled in Libya Murzuk basin (
Yan, Linhui (Petrochina Research Institute of Petroleum Exploration and Development) | Chang, Yuwen (Petrochina Research Institute of Petroleum Exploration and Development) | Tian, Zhongyuan (Petrochina Research Institute of Petroleum Exploration and Development) | Li, Xianbing (Petrochina Research Institute of Petroleum Exploration and Development) | Wang, Li (Petrochina Research Institute of Petroleum Exploration and Development) | Zheng, Xuerui (Petrochina Research Institute of Petroleum Exploration and Development)
Lithology identification in basement rock reservoir is one of the most important basic work for reservoir evaluation. The identification results can directly influence the evaluation of reservoir physical property, oil-bearing property and the identification of effective reservoir.
The paper takes buried hills in Bongor basin as an example to analyze the characteristics of lithologic chemical components and mineral compositions by using core observation, slice identification, geochemical analysis. Based on lithology characteristics, the classification criterion of basement rock was determined. In addition, the log response characteristics were summarized and the corresponding logging identification method was established. The results show that the basement rocks of the research area composed of metamorphic rocks and magmatic rocks. With the decrease of the content of light minerals, the contents of Si and K were decreasing and the contents of Fe, Al, Ti, Mg and Ca were increasing. According to the mineral compositions and contents, the lithologies were divided into 2 categories and 9 subclasses. There were brecciated structure, clasfic structure, gneissic structure, banded structure, net veined structure, augen structure, massive structure and intrusive structure in electrical imaging logging. Meanwhile, logging response characteristics of basement rocks were divided into 6 types combined with the difference of density curve and compensated neutron curve. The established cross plots and summarized characteristics of logging curves and response values could provide a basis for lithology identification. The machine learning approach (SVM) can improve the accuracy of lithological identification.
Congratulations to the four winners of this year’s Imomoh Scholarship, who after careful selection were awarded this scholarship endowed to the SPE Foundation by Egbert Imomoh to support excellence in education for students from the Africa Region. Soneye Temitope is first and foremost an African, then a Nigerian. He hails precisely from Ogere-Remo in Ogun State, Nigeria. He is the only male child in a family of five. He had his primary and secondary education at Mayflower School, Ikenne.
Extensive discoveries of basement hydrocarbon reservoirs have been made in many places of fractured granite and carbonate basement in the world. Important hydrocarbon findings were achieved in fractured granitic basement in Chad and Indonesia by means of UBD and MPD technologies.
The granitic basement in Chad and Indonesia featured with hydrostatic pore pressure gradient with narrow density windows and well developed fractures. The pore pressure coefficient of the basement of Chad was predicted in between 1.02-1.06, and an underbalanced drilling (UBD) technology with a micro-foam drilling fluid was used to make an attempt on reducing drilling fluid losses; the pore pressure coefficient of the basement of Indonesia was estimated to be 1.04, and an underbalanced managed pressure drilling (UB-MPD) technology with a synthetic based drilling fluid was utilized to avoid drilling fluid losses and in favor of hydrocarbon discovery.
Different drilling technologies or modes received different results although drilling in same fractured granitic basement with similar pore pressure. Losses and kicks continued almost all the time during drilling, coring and wireline logging in some wells during UBD in Chad. Losses happened as soon as the rig pump started while overflow occurred no sooner than the rig pump stopped. However, the potential problem of losses and kicks was completely controlled by utilization of UB-MPD technology in Indonesia. No losses were found during underbalanced managed pressure drilling, tripping, connection, and circulation. Nevertheless, both basement hydrocarbon reservoirs in Chad and Indonesia have been obtained important discovery. Crude oil returned to the surface during UBD in Chad and abundant natural gas produced during UB-MPD in Indonesia.
Both UBD and UB-MPD technologies are effective to gain the discovery of fractured granitic basement reservoirs. The underbalanced MPD technology, a precisely pressure controlled drilling system, is able to accurately control the annular pressure profile throughout the wellbore, therefore it could effectively achieve safe drilling in narrow density window and cut non-productive time. It is proved to be more effective and safer in drilling of fractured granitic basement.
Jin, Fu (CNPC Research Institute of Petroleum Exploration and Development & CNPC Drilling Research Institute) | Xi, Wang (CNPC Research Institute of Petroleum Exploration and Development & CNPC Drilling Research Institute) | Shunyuan, Zhang (CNPC Drilling Research Institute)
Located in south of Eastern Venezuela Basin, Orinoco Oilfield is the unique huge ultra-tight oilfield that has not been developed by scale in the world. The high-density tight oil is known for its high content of acids, heavy metals and asphaltenes with a viscosity of 1000-10000mPa·s. ML Block whose OOIP is 178*108bbl is situated in east of the oilfield, while cluster horizontal well drilling and cold production technologies are still under research there.
Based on precise geological researches numerical simulation was carried out to optimize cold production of ultra-tight oil with foamy oil flow patterns in horizontal wells, including optimization of well placement, well spacing and horizontal section length. The near-bit geo-steering drilling technology was applied on adjacent wells to test its performance, while an experiment was conducted with PVT apparatuses to examine the effect of pressure decline rates on foamy oil flow. A long core pressure depletion test was accomplished to reveal the effect of foamy oil flow on recovery factors.
Three-dimension cluster horizontal well drilling and completion technologies shall be applied to develop ultra-tight oil reservoirs in huge loose sandstones, with the near-bit geo-steering drilling technology that controls landing points and horizontal sections in real time, keeping the bit move ahead along the lower boundary of the reservoir. Therefore, recovery rates may be dramatically improved due to the gravity drainage of ultra-tight oil. The most appropriate spacing of horizontal wells (500-600m) and horizontal section length (800-1200m) were determined to achieve the maximum recovery rate. The experiment proves that the recovery rate improves as the formation permeability increases, which means the "worm hole" contributes to heavy oil extraction. Boreholes with relatively large diameters, extensive perforated holes and slotted liners may be used to complete wells. In order to take the most advantages of the foamy oil flow mechanism high displacement ESPs shall be used with the selected thinner squeezed at the bottom, otherwise PC pumps with the thinner added at the wellhead are recommended.
Cold production technologies applied in ML Block save the overall production cost by 15.2%, improving the ultimate recovery rate by 8.6%. The foamy oil flow theory is improved, while it is the first time to integrate foamy oil flow production technologies with cluster horizontal well drilling technologies and near-bit geo-steering drilling technologies. As a result, the overall production rate of tight oil was greatly improved and the average production life of wells was extended.
Congratulations to the four winners of this year's Imomoh Scholarship, who after careful selection were awarded this scholarship endowed to the SPE Foundation by Egbert Imomoh to support excellence in education for students from the Africa Region. Soneye Temitope is first and foremost an African, then a Nigerian. He hails precisely from Ogere-Remo in Ogun State, Nigeria. He is the only male child in a family of five. He had his primary and secondary education at Mayflower School, Ikenne.
Domestic utilization of natural gas in Nigeria is being hampered by the poor developments in the natural gas sector over the years, with low level of electricity (generation) consumption per capital, weak legal, commercial and regulatory framework amidst poor infrastructural developments in natural gas as compared to that which exists for oil. Nigeria ranks the second in gas flaring and shows low volumes of domestic gas utilization, consuming only about 11% out of the 8.25 billion cubic feet produced per day in 2014 despite its natural gas resource endowment.
This paper examines the determinants of domestic utilization of natural gas in Nigeria from 1990-2013. It investigates its relationship as a function of price of natural gas, price of alternative fuels, foreign direct investment, volumes of gas flared, electricity generated from natural gas sources and per capital real GDP. Going further, it forecasts its likely growth rate for a short-term period, using an econometric methodology of ordinary least squares and an ARIMA model, it estimates the relationship between the variables and uses the historical trend to forecast into the future.
The result of the study showed that the determinants jointly explain the pattern of domestic gas utilization in Nigeria by 98%. Individually, per capital real GDP, electricity generated from natural gas sources and changes in the volume of domestic utilization of natural gas was found to have a positive and significant effect on domestic gas utilization. Further, the forecast values show evidence of a slow but gradual increase in utilization pattern in the near future from 2015-2020. A best-case scenario of an increase of 0.15% and a worst-case scenario of a decrease of 0.14% was presented.
In conclusion, having identified significant influences on domestic gas utilization patterns in Nigeria it is imperative that the government uses economic instrument to enhance the utilization patterns in Nigeria by improving economic activities and developing the power sector which shows significant influence in domestic natural gas utilization patterns.
Beyond offshore West Africa where modern densely-sampled data from ships and satellites have played a key role in current understanding of passive margin evolution, Africa is in general rather unevenly known, especially in the subsurface in more remote areas. The GIS-based Exploration Fabric of Africa (EFA, the ‘Purdy project’) was designed to address that problem. It includes structural features such as faults and basin outlines but at a very high and often generalized level, divorced from their underlying genetic linkages. We have undertaken to compile a more detailed tectonic synthesis aimed to integrate understanding of the oceanic margins with the continental realm. This is an overlay to EFA with a variety of public domain, published, non-exclusive, and derivatives of proprietary work at a closer and more detailed level, importantly guided by known patterns of structural styles. Potential field (gravity and magnetic) data provide guidance in locating, extending, and connecting key mapped features; we then rely on the kinematic patterns to predict missing details in a testable interpretation. The result is a detailed structural features map that can function as a framework within which to target and prioritize both conventional and unconventional activity by operators and licensing/regulatory organizations. We illustrate the process in theory and in practice along the Central African Rift System (CARS), where data is sparse. This fault linkage systems approach has flagged underexplored areas where unmapped structure is likely that could, for example, be targeted with hi-resolution geophysical data. A similar system to CARS appears to cross southern Africa from Namibia to Tanzania - a “Southern Trans-African Rift system" or STARS. Exploration in the eastern Owambo Basin resulted in the mapping of a pull-apart basin from depth-to-basement inversion of high-resolution magnetic data and subsequently studied with structural modeling. Thinking in terms of such fault and structural systems, this ‘Kavango Basin’ can be related along strike to the Karoo Basins in Eastern Africa via features such as the Omaruru lineament, implying the possibility of a fairway of extensional basins and shears across the continent that are not obvious in existing low-resolution data. STARS represents a blue-sky frontier concept for both conventional and nonconventional exploration potentially offering new exploration leads, the ultimate objective of big picture work.
Kang, Lin (China National Offshore Oil Corporation (CNOOC) Ltd, Tian Jin Branch) | Wu, Kui (China National Offshore Oil Corporation (CNOOC) Ltd, Tian Jin Branch) | Zhang, Zhongqiao (China National Offshore Oil Corporation (CNOOC) Ltd, Tian Jin Branch) | Guo, Naichuan (China National Offshore Oil Corporation (CNOOC) Ltd, Tian Jin Branch) | Fan, Jianhua (China National Offshore Oil Corporation (CNOOC) Ltd, Tian Jin Branch)
S-shaped strike-slip faults are superposition products of strike-slip and extensional effects, and the deformation zones of the active wall developed along which have been verified as hydrocarbon enrichment areas in many cases of petroliferous basins. Therefore, it is essential to predict the distribution of deformation zones caused by S shaped strike-slip fault. However, there haven’t been methods that can accurately predict them. In this paper, an innovative modeling method is proposed. Firstly, the S-shaped strike-slip fault and strata on its both walls are modeled, strength of strike-slip and extension on which can be adjusted by varying oblique slip angles. Then the active wall of S-shaped strike-slip fault featured by strike slip-extensional, tensional-shear, and extensional-strike slip properties are conducted with forward modeling, based on results of which the distribution model of deformation zones of the active wall can be established. Meanwhile, strata deformation attributes are integrated, which demonstrates restraining and releasing zones as areas favorable for migration and accumulation of oil and gas.
In this study, Liaoxi NO.3 fault, an S-shaped strike-slip fault with extensional-strike slip properties, in the Liaodong Bay, Bohai Bay basin is selected for the case study subject to verify the simulation results. According to interpretation results, on the active wall, fault anticline traps formed in the restraining uplift zones are mainly distributed in the transition part of left to right bends along the fault, while fault block traps formed in the releasing subsidence zones are located in the transition part of right to left bends. Currently, drilling in the restraining uplift zones has received good business effects, which conform to the simulation results. Generally, the forward modeling technology can effectively predict the distribution of restraining and releasing zones, and it can further provide fundamental guidance to the exploration well site deployment.
Presentation Date: Tuesday, October 18, 2016
Start Time: 1:50:00 PM
Presentation Type: ORAL
Drilling through shale formation can be challenging and sometimes results in wellbore instability problems due to the reaction between hydrophilic shale and drilling fluids. The typical low permeability of shale, the presence of ions and charged surface of the constituent clay are factors which makes the problem of wellbore instability very complex despite efforts dedicated to the study by researchers. The study of wellbore stability in shale is quite important because 75% of all formation drilled worldwide are shale formations and 90% of all wellbore instability problems occur in shale formations costing the industry more than $1 billion USD/year (Chenevert, 2002; Zeynali, 2012); the lost time due to this challenge also account for over 40% of all drilling related non-productive time (Zhang et al, 2009) and these instabilities are responsible for 10-20% of the total drilling cost. A solution through this challenge is critical to the sustenance of the investment made by operating companies in the oil and gas industry. This will drastically reduce drilling cost, completion and workover cost as well as the accompanying downtime involved. It will also improve the net present value of operating company in the industry. Basically wellbore instability occurs when the mechanical stress induced by drilling into the formation exceeds the formation rock strength. Chemical interactions between the drilling mud and the in-situ shale affect the in-situ stress state of the formation hence the stability of the formation. Geo-mechanical models have been designed to tackle mechanical wellbore instability in the Niger Delta the challenge therefore is a chemical solution to the wellbore instability problems of the region. Oil-based muds have been known to overcome wellbore stability problems, but disposal challenges and environmental concerns have led to infrequent use. The challenge therefore is to formulate an environmentally friendly drilling mud having the inhibitive properties to tackle the wellbore instability challenges. This paper presents a review of studies carried out to characterize the mineralogy of shales and the salinity distribution of formation water in the Niger Delta depobelts with a view of designing a "balanced-activity" drilling fluid to help stabilize the formation during drilling. Results obtained from the reviewed researches showed that shale mineralogy characterization and formation water salinity distribution is critical in designing a balanced-activity drilling mud that can effectively tackle the problems of wellbore instability.