Baruah, Nabajit (Oil & Natural Gas Corporation) | Mandal, Dipak (Oil & Natural Gas Corporation) | Jena, Smita Swarupa (Oil & Natural Gas Corporation) | Sahu, Sunil Kumar (Oil & Natural Gas Corporation)
This paper examines the prospect of Gas Assisted Gravity Drainage (GAGD) process in improving recovery from a sandstone reservoir by injecting produced gas back into the crestal part of the reservoir. Besides recovery improvement, immiscible gas injection ensures near Zero Flaring strategy. The process has been found to be ideal in reservoirs with high permeability and reasonable dip to maximize oil production wherever a sufficient gas source exists. Based on the study, gas injection is recommended at the crestal part of the reservoir under study at the rate equivalent to the produced gas to maintain pressure, arrest gas cap shrinkage and improve recovery.
Saluja, Vikas (Oil & Natural Gas Corporation LTD.) | Singh, Uday (Oil & Natural Gas Corporation LTD.) | Ghosh, Aninda (Oil & Natural Gas Corporation LTD.) | Prakash, Puja (Oil & Natural Gas Corporation LTD.) | Kumar, Ravendra (Oil & Natural Gas Corporation LTD.) | Verma, Rajeev (Oil & Natural Gas Corporation LTD.)
The case study demonstrated here is the innovative workflow for fault delineation technique on a 3D seismic volume in B-173A Field of Heera Panna Bassein (HPB) Sector, Western Offshore Basin, India. B-173A is located 50 kms west of Mumbai at an average water depth of about 50 m. The field was discovered in the year 1992 and it was put on production in Aug 1998. In B-173A field there are two hydrocarbon bearing zones one is gas bearing Mukta (Lower Oligocene carbonates) Formation and oil bearing Bassein (Middle to Upper Eocene Carbonates) formation.
The present study is an extended workflow on Advanced Seismic Interpretation using Spectral Decomposition and RGB Blending for Fault delineation. Iso-frequency volumes are extracted from Relative Acoustic Impedance data instead of seismic data itself.
The workflow is for effective fault delineation and it consists of Spectral Decomposition of relative acoustic impedance data and RGB Blending of discontinuity attributes of different Iso-frequency volumes.
It is observed that RGB blend volume of discontinuity attributes provided more convincing results for fault delineation as compared to the results of traditional discontinuity attributes.
Mogollón, J. L. (Halliburton) | Yomdo, S. (OIL India Limited) | Salazar, A. (Halliburton) | Dutta, R. (OIL India Limited) | Bobula, D. (Halliburton) | Dhodapkar, P. K. (OIL India Limited) | Lokandwala, T. (Halliburton) | Chandrasekar, V. (CMG)
The perception of better economics and less risk from infill drilling and recompletions are reasons well-focused remedies are preferred compared to reservoir-focused solutions, such as enhanced oil recovery (EOR). However, most literature does not discuss the economic and risk indicators driving this.
Using a real example, this work demonstrates that combining polymer flooding with infill drilling and recompletion substantially increases economic benefits with reasonable risk.
The reservoir considered is an Oligocene sandstone at a depth of 2700 m. The °API is 29.5 and permeability ranges from 50 to 500 mD. Current reservoir pressure is 43% of the original and it is below bubble point. A black oil model with a 133 × 56 × 128 grid was used. The model incorporated more than 50 years of matched primary and waterflooding production history and experimental polymer physico-chemical parameters. For the stochastic economic risks estimation, 1,000 iterations were run for each scenario considering uncertainties in injection-production, capital expenditures (CAPEX), operational expenditures (OPEX), and oil prices.
For a 20-year horizon, the injection-production-pressure profiles were numerically forecasted; economic results were calculated using a classic model and inputs from the forecast. The economic risk was determined stochastically. The redevelopment scenarios considered were as follows: Base: current waterflooding Existing wells interventions: workover, opening shut-in wells, and new perforations Infill drilling: vertical/horizontal infill drilling wells + existing wells operations Polymer flooding: using existing wells Combined Infill and polymer: vertical infill drilling wells and polymer flooding
Base: current waterflooding
Existing wells interventions: workover, opening shut-in wells, and new perforations
Infill drilling: vertical/horizontal infill drilling wells + existing wells operations
Polymer flooding: using existing wells
Combined Infill and polymer: vertical infill drilling wells and polymer flooding
P50 forecasts showed that interventions in existing wells in the base scenario increased oil production by 11% and net present value (NPV) by 71% with a risk index of 0.38.
A numerical optimizer was used to account for possible combinations of 14 potential drilling locations and vertical to horizontal well ratios. A scenario with three vertical wells was selected. Compared to the base case, this scenario showed an oil production increase of 23%, NPV increase of 178%, and a risk index of 0.41.
The injection rate of the polymer flood was optimized, resulting in a 17% increase in oil production and 95% increase in the NPV, with a risk index of 0.40. This justifies performing a polymer flood.
The most promising scenario is the combined infill drilling and polymer injection, which significantly improved the economic indicators—30% increase in oil production, 230% improvement of the NPV over the base scenario, with a risk index of only 0.41.
The results of this study demonstrate that the combination of EOR with different operational strategies results in significant benefits compared to the individual scenarios. Analysis of just oil production independent of economics and risk can be misleading. Infill drilling or flooding should no longer be the question. Instead, the question should be how they can be properly combined at various stages of asset life.
PY-1 is one of the few fields in India producing hydrocarbons from Fractured Basement Reservoir. The field was developed with nine slot unmanned platform with gas exported through a 56 km 4" multiphase pipeline to landfall point at Pillaperumalnallur. Field was put on production in November 2009 with three extended reach wells. The production performance of the field had some surprise and declined earlier than expected. As a result, based on the conclusions drawn from an integrated subsurface study, a two wells reentry campaign to side track wells Mercury and Earth was planned to be executed in Q1 2018. The objectives of this paper are twofold: 1. Review the production performance of a granitic basement gas field and share learnings which may be useful for similar fields being developed elsewhere.
Biswal, Debakanta (Adani Welspun Exploration Limited) | Nedeer, Nasimudeen (Adani Welspun Exploration Limited) | Banerjee, Subrata (Adani Welspun Exploration Limited) | Singh, Kumar Hemant (Indian Institute of Technology)
The boundary between a thick carbonate layer and its substrata is often a well-defined reflector due to the presence of shaly and clayey layers beneath the carbonates. This reflector and other underlying reflectors result in a velocity pull-up effect because the seismic velocities within the carbonates are higher than that of the surrounding sediments. The geometry of velocity pull-up beneath the carbonate body is related to the geometry of the structure and the thickness of the carbonate body the seismic wave travels through.
In B9 area of Mumbai Offshore basin, the reservoir facies are largely represented by clastics deposited along tidal deltaic lobes. Wells drilled though Daman formation have encountered good quality pay sands within the Daman formation. This pay has produced commercial quantities of hydrocarbons in the vicinity making the area attractive for further exploration and exploitation. The overlying Bombay formation consists mainly of shale with occasional bands of limestone and claystone. The development of thick isolated carbonates bodies within Bombay formation is observed in "C" structure on which "Well-C" is placed. This is seen to significantly constrain the structural configuration in the "C" area. There is a possibility of substantial extension of the "C" structure towards south if the impact of velocity pull up due to carbonate build up can be successfully mitigated. The ultimate challenge is to image the Daman reservoirs, mitigating overburden lateral velocity variations.
In addition to a layered cake depth conversion approach for depth conversion of the time map, a more robust approach, PSDM followed by depth conversion was carried out. This paper highlights the merit of different methods.
This paper attempts to use analogs of coals and Coal bed Methane (CBM) properties in Sedimentary basins to mutual advantage from the knowledge of each other.
An attempt has been made here to showcase as to why two Coal bearing formations, Lower Eocene, Cambay in India and Miocene, South Sumatra, Indonesia can be compared with each other in terms of coal quality and CBM characteristics.
Cambay basin, with an area of 56,000 sq kms is an elongated NNW-SSE rift basin in the western part of India. The basin fill comprises Mesozoic(?) sediments capped by Late Cretaceous Deccan volcanics and a thick tertiary pile of fluvio deltaics. Thick Lignite to sub bituminous coal is found in Middle (two thick seams) and Lower Eocene section (three thick seams of 20-35 m range and one thin seam of 1-10m). Chemically, the Middle Eocene lignite-sub bituminous coal is characteristically low in moisture (4-5%), quite low in ash (1-11%) and high in volatiles (43-55%). The Lower Eocene coals are sub bituminous with 10-20% moisture, low ash(5-10%), low Sulphur(<1%) content. The gas content of the Lower Eocene coals are 6 cubic metre / tonnne, with permeability 1-3 Md with seams slightly over pressured. Depth ranges of both these coal horizons are between1000-1800m approximately.
South Sumatra basin, double in size wrt Cambay basin with an area of 100,000 sq kms, is a NE-SW trending, backarc basin. Series of half grabens punctuated with basement highs, holds Miocene and Eocene Coals in the grabens of a mostly Tertiary sedimentary pile. The Miocene coals (formed in tide dominated coastal plain) are sub bituminous, with VRo 0.4-0.5, low ash(<10%), Moisture(10-18%), high volatile matter of around 40% at depths 300-1000m, with 20-30 seams with gas content of 7 cubic metre / tonne. The Older Eocene Coals are1-10 m thick at depths 1000-2000m formed in peat bogs in fluvial settings.
The Indonesian Coals of Miocene age are very comparable in coal properties and gas content to the Middle and Lower Eocene Coals of Cambay basin and can supplement each other in studies for CBM exploration and exploitation. Of great similarity are the coal quality, ash% and gas content. To take the comparisons further ahead, detailing of thickness, extent, geometry and depositional environments of each of these basins would be advantageous.
Panna Formation is a very critical and challenging formation deposited during Paleocene time of geological past in various parts of Western Offshore Basin of India. It was deposited in a fluvio-deltaic environment, sometimes even in a restricted marine set-up. Such variation in depositional setting caused mineralogical complexity, which in-turn imposed a limitation in conventional approach of formation evaluation and saturation determination to identify the pay zones with confidence. A comprehensive approach of integrated formation evaluation for rock quality characterization was attempted using a combination of new generation elemental and acoustic analysis for delineating the potential hydrocarbon bearing zones independent of conventional resistivity-based approach along with a better insight on formation heterogeneity. The studied well was drilled up to Panna Formation and conventional open-hole logs were acquired while drilling. However, due to complex mineralogical nature of the formation, estimation of key critical reservoir parameters was very challenging and imposed higher uncertainties in the results. An alternate approach was adopted using a few advanced log measurements to address this challenge. A combination of new generation elemental and acoustic data has been recorded in a single wireline run after acquiring conventional basic logs while drilling. An accurate porosity was derived by eliminating various mineralogical assemblages along with estimation of a geochemical permeability based on detailed elemental analysis. Measured aluminum from neutron inelastic capture spectrum method enabled to estimate clay volumes with accuracy, which provided the required insight for better effective porosity in such shaly-sand environment. Based on this improved porosity and permeability, an approach for rock-quality indexing was used for reservoir delineation.
Moreover, a good amount of organic carbon was found associated with clays caused shales with higher resistivity. Based on elemental measurements an interesting insight was possible to extract for resistivity independent fluid saturation. An additional pay zone with hydrocarbon saturation based on such resistivity independent approach was possible to identify, which was masked by conventional resistivity-based interpretation. Acoustic analysis results assisted in delineating the zones with possible open fractures to avoid any possibility for unwanted fluid breakthrough.
Based on this approach of alternate integrated petrophysical analysis perforation zones were selected including an additional zone, which was masked based on conventional analysis. The well was started producing around 1,05,000 m3 gas with around 200 barrels of oil per day. This study showcased an alternate and efficient characterization approach for any such mineralogically challenging clastic formations.
Arisandy, Mellinda (PETRONAS Carigali Indonesia Operations) | Mazied, Miftah (PETRONAS Carigali Indonesia Operations) | Putra, Bayu P (PETRONAS Carigali Indonesia Operations) | Yogapurana, Erik (PETRONAS Carigali Indonesia Operations) | B Mohd Idris, Jamin Jamil (PETRONAS Carigali Indonesia Operations) | Darmawan, Hendra I. (PETRONAS Carigali Kuala Lumpur)
This paper describes geochemistry analysis, hydrocarbon charge and entrapment model for prolific "MA" Block in the West Natuna Basin. Even though the area is currently at a mature exploration stage, the behaviour of hydrocarbon distribution in the area is still poorly understood and the link between discovered hydrocarbon and possible kitchens is still unknown. This study is an attempt to understand hydrocarbon expulsion, charging and entrapment in "MA" Block to de-risk further exploration efforts.
Several localized inverted half-grabens were identified through seismic interpretation. Nearby wells were then selected in evaluating source rock quality and maturity. In order to determine hydrocarbon expulsion model, 1D-3D burial history and thermal maturity models were constructed using integration of source rock and fluids geochemistry, temperature, seismic, and well data. Hydrocarbon charge and entrapment models were then simulated using 3D basin modeling software and calibrated with existing proven accumulation to produce a risked understanding of hydrocarbon distribution in the study area.
This study suggests that the most possible source rocks are the Late Eocene and Oligocene shales of Lama Formation and Lower Gabus Formations. Both source rocks are indicated by type I & type III kerogen. Lama source rock was confined in the initial grabens and post mature in deep paleo-grabens. This study confirmed that charging is derived from four (4) kitchen areas: Anoa, Gajah, Kakap, and Kambing grabens. The oil samples from "MA" Block indicated lacustrine facies. Rock geochemistry analysis portrayed oil-prone and gas-prone source rock.
In general, hydrocarbon was migrated from the southeastern area (Kambing graben) and southwestern area (Gajah graben). Hydrocarbon was later on accumulated in the nearest structural entrapments (anticlines). In the deep grabens (Kakap and Kambing), the hydrocarbon expulsion was starting as early as 37 Ma and 31 Ma, respectively, while in shallow graben (Anoa) the expulsion was starting at 29 Ma. The earliest structural trap commenced at 21 Ma, aligned with the initial compressional regime that was affecting the West Natuna Basin. Notable accumulative erosion in Miocene was nearly 1000 m at inverted structures, by which partly removed regional seal and reduced reservoir effectiveness. Significant yet-to-find hydrocarbon is predicted to be concentrated in the Anoa, Kakap, and Northeast Kambing area.
Cai, Junjie (Shenzhen Branch, CNOOC China limited) | Wen, Huahua (Shenzhen Branch, CNOOC China limited) | Gao, Xiang (Shenzhen Branch, CNOOC China limited) | Cai, Guofu (Shenzhen Branch, CNOOC China limited) | Hu, Kun (Shenzhen Branch, CNOOC China limited)
Huizhou Depression is in the exploration peak stage at present. The main target layer is gradually extending from the middle-shallow traps to the deep paleogene traps and the shallow lithologic traps, and the difficulty of exploration is totally increased. Paleogene layer oil&gas exploration is faced with the problems of deep buried depth, reservoir heterogeneity and uncertain distribution of high-quality hydrocarbon sources.
By combining tectonic evolution analysis with sequence stratigraphy, considering regional stress background and the utilizing of the seismic facies, the main faults tectonic features, stratigraphic sedimentary characteristics, the distribution position of sedimentary center and the control effect of the palaeogeomorphology on the sedimentary distribution range deposited from the transition zone are analyzed.
It is concluded that the lower Wenchang period's tectonic movement was dominated by the southern depression control fault, and the semideep-deep lacustrine high-quality hydrocarbon source rocks were mainly distributed in the south of the Huizhou Depression, such as HZ 26 Sag and the subsag of the XJ30 Sag. The braided river delta deposited from XJ30 transfer zone is mainly distributed along the west side of the long axis of XJ30 sag, and the semideep-deep lacustrine facies mudstone is formed in the east of XJ30 Sag. In the upper Wenchang period, the activity of the depression control faults in the northwest of the Huizhou Depression becomes stronger than the south, which influences the sedimentary center migrated from southeast to the northwest. The sediment provenance of XJ30 transfer zone deposits perpendicular to the long axis of the XJ30, and the long braided river delta is formed in the south side of the XJ24 Sag. In Enping period, which is changed from strong rift phase to rift-depression transition phase, the shallow lacustrine-swamp facies are taken as the main source rocks, and shallow braided river delta is widely developed, while the sediment from the provenance of XJ30 transfer zone is weakened.
The northern and southern migration of the transfer zone provenance river delta and the northern and southern distribution characteristics of the source rocks of semideep-deep lacustrine facies are caused by the differences of the northern and southern fault activities during the Paleogene period. Through the combination of structural evolution analysis and sedimentary characteristics analysis, the analysis of paleogeomorphology's effect on the control of sedimentary system is of great importance to the identification of high-quality paleogene reservoirs and hydrocarbon sources.
Overpressures (abnormally high fluid pressures) represent a significant geohazard and drilling problem. Prediction of overpressures is very important for well planning and safe drilling. However, accurate and reliable prediction requires an understanding of the origins and distribution of such overpressures. Petrophysical properties of the sediments are affected by different overpressure generation mechanisms and in turn help in understanding the types of such mechanisms. There are two distinct overpressure generating mechanisms, namely compaction disequilibrium (undercompaction) and fluid expansion (unloading), each of which have different petrophysical signatures and hence different prediction methodologies. The most common cause of overpressure generation in the majority of the sedimentary basins in the world is undercompaction, in which pressure increases due to rapid burial/loading of the sediments in an effectively sealed impermeable environment. This type of overpressure is normally associated with abnormally high porosities and shows up in changes in velocities. The secondary type of overpressure mechanism is fluid expansion. Thermal induced overpressure is the most common fluid expansion mechanism. This mechanism is very common in areas of high geothermal gradient and can result in significant overpressures. This mechanism, however, is not always present. Thermally induced overpressures result in decreasing effective stress in contrast to overpressure due to undercompaction where a constant effective stress is observed. Thermally induced overpressures are difficult to predict and require a different prediction methodology. Improved knowledge of overpressure generating mechanisms and distribution of pore pressure in a basin provides critical supporting information for the asset team in hydrocarbon exploration and production. This information not only has an immediate impact on drilling cost and safety but also provides insight to key elements in petroleum system analysis.
This paper presents a study showcasing the geological control on origin and distribution of overpressure in a HPHT (high pressure, high temperature) field from offshore (water depth ~100-150m) South East Asia. Historically, the offset wells in the field were drilled through complex geological settings including high overpressure (~17-18 ppg), high temperature (170-185 deg C) and variable stress fields. The lithology is dominated by shales and most of the wells drilled in the area encountered drilling challenges with respect to high overpressure development. An initiative for a pore pressure prediction study was undertaken in a semi-regional scale involving ten offset wells in the study area. The main focus was to understand the overpressure mechanism and distribution in the study area vis-à-vis the geological setting and control. This was followed by predrill prediction for the planned wells, as one of the objectives of this study was also to aid in future development well drilling. Well planning based on the study results were done for two prospect wells which were located in similar shallow water.