In the Midland Basin of west Texas, produced water volumes have historically been disposed into shallow intervals (i.e., Grayburg-San Andres). Over the last decade, the rapid growth in unconventional resource development has resulted in a significant increase in the volume of produced water leading to pressure gradient differences between shallow disposal zones and deeper intervals. These conditions have created drilling challenges and have prompted operators to test additional zones suitable for produced water disposal. In recent years, the Early Ordovician Ellenburger (ELBG) reservoir has become an alternative disposal interval to shallower reservoirs.
The Ellenburger Group of west Texas, a prolific producing reservoir, is part of an extensive carbonate system best known for karst development associated with prolonged subaerial exposure and intervals of high secondary porosity in fracture breccias generated by subsequent cave collapse. Many authors have described fracture occurrence and karst-related breccias of the ELBG, both of which impact productivity at the reservoir scale within the fields and make regional correlations particularly challenging. Ellenburger depositional facies have been described by previous workers in equivalent units across west and central Texas, and textural analysis of high-resolution electrical borehole images from recently drilled disposal wells, combined with core observations, shows corresponding porous intervals to be present in the Midland Basin.
This paper describes the generation of a regional model of porosity distribution within the Ellenburger and assesses the important differences in depositional environment and diagenetic history that exist among the internal units of the ELBG that may impact salt water disposal (SWD) well performance. For example, the Upper ELBG is dominated by fracture porosity in breccia fabrics associated with collapsed cave systems, while the Lower ELBG exhibits preserved porosity associated with original depositional textures. The regional model was tested using multiple datasets: image logs, core descriptions, electric logs from more than 400 well penetrations, and injection data from recent well tests. The integration of these datasets has resulted in a suite of maps of the key stratigraphic intervals within the ELBG that offer the greatest potential for disposal. Additionally, the integration of well performance with observed regional geologic trends was used to identify and tier key performance drivers for deep SWD injection performance, resulting in refined performance maps that can be used for strategic placement of deep SWD wells.
Zhang, Yiming (CNPC Huabei Oilfield Company) | Tian, Jianzhang (CNPC Huabei Oilfield Company) | Yang, Dexiang (CNPC Huabei Oilfield Company) | Chen, Shuguang (CNPC Huabei Oilfield Company) | Liu, Xing (CNPC Huabei Oilfield Company) | Hou, Fengxiang (CNPC Huabei Oilfield Company) | Tian, Ran (CNPC Huabei Oilfield Company) | Zhang, Chuanbao (CNPC Huabei Oilfield Company)
The study area is located in the Langgu sag of Northern Jizhong depression, Bohai Bay Basin, East China. In order to achieve exploration breakthrough in deep buried hill, key engineering technologies are developed and used to accurately demonstrate important target identification by recognizing new hydrocarbon accumulation patterns resulting from the analysis of multi-stage structure-controlled trap mechanism and the detailed study of controlling factors over high-quality Ordovician reservoirs based on new high-accuracy 3D seismic data. This study reveals a new evolution mechanism of buried hill controlled by structural superposition, experiencing "the uplift from thrusting in Indo-Chinese to early Yanshan epoch, uplifted block faulting into horsts in middle Yanshan epoch, horsts tilting into belt in Eocene, and belt reversion into trap", and thus puts forward a new mechanism for reservoir forming controlled by a superposition of "dolomite, karsting, and faulting". Three types of reservoir development are identified, including "regional layered pore, local block micropore-fracture, and fracture hole pore layer-block composite", and an accumulation pattern in deep buried hill is constructed, characterized by "efficient hydrocarbon supply from gas-type source rock, predominant migration through fractured surface-nonconformity surface, and stratum- and mass-controlled accumulation", which has guided the 40 years' exploration of Ordovician Yangshuiwu buried hill zone and made a great breakthroughs. Novel relevant exploration technologies have been developed, involving high-accuracy imaging, high-precision well logging identification of hydrocarbon reservoir, ultra-high temperature deep drilling and completion, ultra-high temperature carbonate reservoir stimulation, etc, which solve a worldwide problem that has restricted the exploration of the ultra-high temperature buried hill for many years. These technologies make possible the highest daily production of over 100 m3 oil and 0.5 million m3 gas respectively and sustain a high and stable production for a long term, which guarantee the clean energy supply for Beijing-Tianjin-Hebei region.
The Cambro-Ordovician succession of Saudi Arabia comprises dominantly siliciclastic sediments deposited in a passive margin intracratonic setting and includes the fluvial to marginal marine Saq Formation (Late Cambrian to early Middle Ordovician), the marine Qasim Formation (late Middle to Late Ordovician) and the glaciogenic Sarah Formation (Hirnantian, latest Ordovician). The Saq Formation is subdivided into the Risha Member (Late Cambrian) and the Sajir Member (Early to Middle Ordovician). Palynological age-control in the Risha Member is provided by a characteristic acritarch assemblage (CB1 Palynozone) which contains well-known Furongian (Late Cambrian) diagnostic taxa (e.g., Trunculumarium revinium, Timofeevia phosphoritica and Ninadiacrodium dumontii), as recorded in one subsurface locality in the Arabian Gulf. This typical assemblage occurs worldwide in Furongianaged strata and not only permits a confident age-attribution, but also indicates an open marine facies within the predominantly fluvial to marginal marine lower Saq Formation. In Oman, the same assemblage occurs in the Al-Bashair Member of the Andam Formation. In the lower part of the Sajir Member, one acritarch assemblage characterized by the presence of Acanthodicaodium angustum and Vulcanisphaera spp., was described from a subsurface section in Eastern Saudi Arabia, indicating an earliest Ordovician (Tremadocian) age. This assemblage forms the O6 Palynozone and suggests correlation with the Mabrouk Member of the Andam Formation in Oman.
Cao, Chuan (CNPC CPET) | Luo, HuaiDong (CNPC Interational Chad Co., Ltd.) | Zhang, QuanLi (CNPC CPET) | Xu, BingGui (CNPC CPET) | Zhang, YanPing (CNPC CPET) | Jia, Tao (CNPC CPET) | Yu, YongLiang (CNPC CPET) | Yin, HongWei (CNPC CPET) | Wang, JianLi (CNPC CPET)
Water encroachment is considered main reason for production decline on Carbonate reservoirs which are trapped in deep, HTHP formations in Tarim Basin, after early development stage. Sidetracking re-entry horizontal wells is a cost-effective way to recover oil production from existing mature fields. However, the unstable formation and variation in formation pressures during re-entering posed extremely challenging problems which drive well costs up and even jeopardize reaching total depth. The operator launched a work over campaign to re-enter old wells, sidetracking through 7"casing to the target Ordovician reservoir. The unstable Carboniferous Formation lying above and different pressure regimes (high pressure on Carboniferous formation; low pressure on Ordovician reservoir) significantly reduce the probability of operation success. A Solid expandable solution was selected to case off the high pressure and unstable zone. This paper reviews three case histories of solid expandable liner installations on horizontal sidetracking wells. The maximum expandable liner installation depth reached almost 20,000ft, at deviated 65.8 deg. well section with 1,728ft expandable liner expanded. The expandable liner isolated the high pressure Carboniferous Formation, this enabled the operator to drill the reservoir with lower mud weight while minimizing the risk of differential sticking, and conserved valuable hole size to allow the logging program to be conducted as desired and produce through larger diameter production tubular. Solid expandable solution has demonstrated as the best option to meet the objectives for re-entry deep horizontal wells.
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 (
The Hoban and Baqaa Members are located between the glacial to early post-glacial Sarah Formation (Ordovician) and the Qalibah Formation (Silurian). They have been distinguished as separate stratigraphic units in few outcrops of northern Saudi Arabia based on palynological analyses, graptolites, shell fragments, and their predominantly shallow marine depositional environments. There has been long debate over whether the Hoban and Baqaa Members should be attributed to other upper Sarah Formations or the lower Qalibah Formation. This debate fundamentally concerns the location of the Silurian-Ordovician sequence boundary, which developed globally, in central Arabia. Detailed sedimentological and stratigraphical data of the latest Ordovician to earliest Silurian interval were available from the subsurface. Therefore, the main aim of this project is to provide a detailed sedimentological model for the Hoban and Baqaa Members, both in outcrop-reservoir analogues and in the subsurface. This includes a sequence stratigraphic correlation between outcrops and wells, and general depositional environment maps. The resulting model provides an improved understanding of depositional changes as well as relative and eustatic sea-level changes across the Ordovician-Silurian boundary in Arabia.
The study is based on 16 outcrop sections in three different regions of northwestern and northeastern Saudi Arabia (Tabuk, Tayma, and east of Hail) and 26 shallow and deep well cores. Outcrops and the well are enclosed in a total area of about 340 by 100 km. The Hoban Member has a thickness between 0-40 m (typically 23 m) and consists of two units, which represent the final stages of glaciation. Sediment deformation, internal brecciation, and angular Sarah clasts are widespread. The Baqaa Member, which has a thickness of 15-40 m (typically 31 m), unconformably overlies the Hoban Member and consists of two to three shallowing-upward cycles (high-frequency sequences). Each cycle consists of a basal transgressive part (proximal offshore) and a regressive part (lower to upper shoreface or foreshore, respectively). The top of each cycle is formed by closely stacked submarine hardgrounds (transgressive surface at the base) with ample bioturbation and shell horizons. Hot shales of the Qusaiba Member (Qalibah Formation) conformably cover the hardground of the upper Baqaa shallowing-upward cycle. Palynological data indicates that both the Hoban and Baqaa are late Ordovician in age, while the Qusaiba shales are lower Silurian.
The Hoban Member represents stages of final glacial advance and local sediment mass transport in a peri-glacial environment. The Baqaa Member represents post-glacial flooding with prograding beach and shoreface systems. During peak transgression, intermittent open marine conditions existed. Long-term fully marine conditions were only established in the lowermost Qusaiba Member. From a process-oriented perspective, the Hoban Member constitutes the uppermost member of the (peri-) glacial Sarah Formation, the Baqaa Member as the lowermost member of the post-glacial Qalibah Formation.
Wang, Hongqiu (PetroChina Research Institute of Petroleum Exploration & Development-Northwest, Lanzhou, Gansu, China) | Liu, Weifang (PetroChina Research Institute of Petroleum Exploration & Development-Northwest, Lanzhou, Gansu, China) | Gao, Jianhu (PetroChina Research Institute of Petroleum Exploration & Development-Northwest, Lanzhou, Gansu, China) | Li, Shengjun (PetroChina Research Institute of Petroleum Exploration & Development-Northwest, Lanzhou, Gansu, China) | Gui, Jinyong (PetroChina Research Institute of Petroleum Exploration & Development-Northwest, Lanzhou, Gansu, China) | Guo, Xin (PetroChina Research Institute of Petroleum Exploration & Development-Northwest, Lanzhou, Gansu, China)
Two sorts of ancient water patterns that surface water pattern and underground water pattern exist and develop near the Ordovician carbonate buried hill in Tarim Basin. Frequency mixing technique can effectively improve the resolution effect of the frequency division result attribute of single frequency, which is more effective in detailed identifying the surface and underground river. Both surface river pattern and underground river pattern can form effective karst space, which provides important proof for revealing the development law of the Ordovician ancient karst in Tarim Basin. Underground river pattern controls the distribution of large karst cavity, and poses significant impact on the formation of top large collapse fractures due to cavity collapse in later stage; surface river pattern has mainly invasion effect at the buried hill high parts and lateral and vertical corrosion at low parts, however, deep corrosion can be formed on both sides and riverbed. During the process of diagenesis, fractures are formed due to later filling and overburden differential compaction. The study on ancient river pattern poses significance for revealing karst distribution law, deepening non-tectonic fracture study and expanding exploration of fractured reservoirs.
Presentation Date: Monday, October 15, 2018
Start Time: 1:50:00 PM
Location: Poster Station 5
Presentation Type: Poster
Zhang, Sheng (Institute of Tarim Oilfield Company, Petrochina) | Cui, Deyu (Institute of Tarim Oilfield Company, Petrochina) | Li, Pengfei (Institute of Tarim Oilfield Company, Petrochina) | Yang, Pengfei (Institute of Tarim Oilfield Company, Petrochina) | Gao, Lianhua (Institute of Tarim Oilfield Company, Petrochina) | Wang, Xinxin (Institute of Tarim Oilfield Company, Petrochina)
Many studies imply that when the rocks are saturated with different types of fluid it generally expected to have different magnitude of attenuation and dispersion. It is attractive to use this property to discriminate different fluid types with seismic data. In this paper, the real seismic cases are from Northern Tarim Oilfield, west of China, the Ordovician carbonate reservoir which is quite different from the pore spaces in sandstone reservoir, and the characteristics of carbonate reservoirs are solution caves and fractures. We can use the maximum trough amplitude to determine the locations of solution caves, while the solution caves always contain different fluids, sometimes it is difficult to make sure which cave is saturated with hydrocarbons especially when the area is under a complex geological condition. In order to overcome this problem, we combined conventional geology analysis with the technology of smoothed pseudo Wigner-Ville distribution (SPWVD) which is used for spectral decomposition intended to get the high precision time-frequency energy distribution. Compared with the strong energy of the solution caves, the high amplitude energy groups caused by elastic interfaces can be eliminated by normalization, the reserved amplitude energy of the caves vary with frequency can discriminate oil and water. The exploratory wells show that this method makes it possible to successfully predict the fluid types of the carbonate reservoirs.
Presentation Date: Thursday, October 18, 2018
Start Time: 8:30:00 AM
Location: 209A (Anaheim Convention Center)
Presentation Type: Oral
Chen, Peng (CNPC Engineering Technology R&D Co. Ltd.) | Zhou, Yingcao (CNPC Engineering Technology R&D Co. Ltd.) | Liu, Wei (CNPC Engineering Technology R&D Co. Ltd.) | Wang, Junjie (CNPC Chuanqing Drilling Engineering Co. Ltd.)
It is effective to drill horizontal wells in carbonate to increase production. However, the horizontal sections were limited and hard to be extended by means of conventional drilling due to high risk of drilling in fractured cavernous carbonate. Application of a precisely pressure controlled drilling system was developed to have successfully drilled and extended horizontal sections, reduced risk of drilling in the said kind of wells with narrow pressure margins in western China’s Tarim basin.
A comprehensive MPD technology with 9-operational situations, 4-controlling modes and 13-precise controlling techniques of emergent changeovers was built up through full-size laboratory test, field test and deployment. Under-, near-, or over-balanced MPD was selected and carried out to meet diversified requirements based on proper well trajectory design, build-up rate control, retention of margin for adjustment and control of the well track, dynamic prediction of bottomhole pressure alternation while drilling according to the stability of the formation and whether toxic gases existed.
Drilling in Tarim basin usually experienced complex geology, narrow density margin, low ROP, frequent downhole complex and accidents, and long drilling duration. After the precise MPD technology being applied in Tarim basin, the risk of kick-and-loss coexistence has been reduced and the well cost has been gained beneficial results. The application assisted not only the hydrocarbon discovery of reef flat geology of Ordovician system in China’s Tarim basin, but also the well deliverability enhancement, effective treatment of downhole complex, and improvement of ROP. Application of precise MPD in a Tarim horizontal well created a record for deepest horizontal well with MD at 8,008m, TVD at 6,327m, and horizontal section of 1,551m. Another Tarim horizontal well produced a new record of daily footage 150m and horizontal footage 1,561m, and 42 pay zones were discovered. The difficulty of horizontal section pressure control in fractured cavernous carbonate was effectively resolved and multi combinations of fractures and caves were drilled through by application of precise MPD technology. The horizontal sections, historically limited by 200m-300m, were largely extended in fractured cavernous carbonate horizontal wells, and the well capacities were advanced.
Drilling of fractured cavernous carbonate horizontal wells is an integration and innovation of the precise MPD technology, downhole risk control, and the optimization and control of horizontal well trajectory. The precise MPD technology could effectively avoid or alleviate downhole risk, cut non-productive time, extend horizontal section, promote rate of penetration, reduce drilling cycle, achieve safe drilling, and therefore reduce well cost. It would play a significant role in future challengeable drilling activities.
Liu, Qing-You (Southwest Petroleum University and State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation) | Tao, Lei (Southwest Petroleum University and State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation) | Zhu, Hai-Yan (Southwest Petroleum University and State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation) | Lei, Zheng-Dong (PetroChina) | Jiang, Shu (China University of Petroleum (East China) and University of Utah) | McLennan, John D. (University of Utah)
Waterless fracturing for shale-gas exploitation using supercritical carbon dioxide (scCO2) is both effective and environmentally friendly, and has become an extensive research topic. Previous researchers have focused on the chemical and physical properties and microstructure of sandstone, carbonate, and shale caprock, rather than on the properties of shale-gas formations. The macroscale mechanical properties and microscale fracture characteristics of Wufeng Shale exposed to scCO2 (at greater than 31.8°C and 7.29 MPa) are still not well-understood. To study the macroscale and microscale changes of shale subjected to scCO2, we obtained Chinese Wufeng Shale crops (Upper Ordovician Formation) from Yibin, Sichuan Basin, China. The shale samples were divided into two groups. The first group was exposed to scCO2, and the second group was exposed to nitrogen (N2). Scanning-electron-microscope (SEM) and X-ray-diffraction (XRD) images were taken to study the original microstructure and mineral content of the shale. To study the macroscale mechanical changes of Wufeng Shale immersed in scCO2 or N2 for 10 hours, triaxial tests with controlled coring angles were conducted. SEM and XRD images were taken after the triaxial tests. In the SEM images, tight bedding planes and undamaged minerals (with sharp edges and smooth surfaces) were found in N2-treated samples both before and after testing, indicating that exposure to N2 did not affect the microstructures. However, the SEM images for the microstructure scCO2-treated samples before and after testing were quite different. The bedding planes were damaged, which left some connected microfractures and corrosion holes, and some mineral types were broken into small particles and left with uneven mineral surfaces. This shows that scCO2 can change rock microstructures and make some minerals (e.g., calcite) fracture more easily. The complex microscale fractures and the decrease in strength for scCO2-treated shale aid the seepage and gathering of gas, enhancing shale-gas recovery. Knowledge of the multiscale physical and chemical changes of shale exposed to scCO2 is not only essential for scCO2 fracturing, but it is also important for scCO2 jets used to break rock and for the geological storage of CO2.