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Collaborating Authors
Bhardwaj, Nitin
Abstract Drilling and reaching to deeper target zones through an overpressured overburden formation in a structurally complex geologic setting requires robust geologic and geomechanical analysis to mitigate risk and control operational costs. These types of geologic conditions are present in the Krishna-Godavari Basin, where a series of horst and grabens defined by deep-seated faults and persistent high sedimentation rates through geologic time, result in the development of challenging conditions for exploratory drilling. We have developed possible overpressure mechanisms across the central part of the Krishna-Godavari Basin and its interplay through fault-related lateral pressure transfer. The basin sits over a horst, which is one of the many northeast–southwest-trending en echelon horst and graben structures comprising sediments from the lower Cretaceous to Holocene. In the study area, Paleocene formations in the horst are overpressured (12–12.2 ppg). Three wells were drilled through this formation and reached the target without any drilling issues in the central and eastern part. However, the same formation in the western part of the horst (adjacent to the graben) has higher overpressure of approximately 14 ppg, which complicates the drilling operations because it requires an additional intermediate casing to reach the target reservoir safely. A detailed analysis of the overpressure mechanisms across the horst area to the adjacent deep graben revealed that the disequilibrium compaction signatures are related to the burial history and overburden thickness. The major difference between horst and graben area is the magnitude of overpressure, with an average of 16 ppg across the graben area. The larger overpressures experienced toward the western part of the horst indicate a secondary source of pressure from the adjacent deep graben. The fault stress analysis in this region presents a feasible lateral pressure transfer through critically stressed faults/fractures from the deep graben to the western part of the horst structure. The current model accounts the common pore pressure estimation method along with other critical geologic information to predict such overpressure related challenges in the upcoming future wells in a similar geologic setup to plan safe and cost-effective wells.
- Phanerozoic > Mesozoic > Cretaceous (0.69)
- Phanerozoic > Cenozoic > Paleogene > Paleocene (0.53)
- Phanerozoic > Cenozoic > Quaternary (0.48)
- Geology > Structural Geology > Tectonics > Extensional Tectonics (1.00)
- Geology > Structural Geology > Fault > Dip-Slip Fault > Normal Fault (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.48)
- Geophysics > Seismic Surveying (0.70)
- Geophysics > Borehole Geophysics (0.68)
- Oceania > Australia > Western Australia > Perth Basin (0.99)
- North America > United States > West Virginia > Appalachian Basin > Marcellus Shale Formation (0.99)
- North America > United States > Virginia > Appalachian Basin > Marcellus Shale Formation (0.99)
- (15 more...)
Integration of Drilling, Geology and Geophysical Data: Developing High Resolution Predrill Wellbore Stability Model for Ultra-Deepwater Field Development
Kumar, Ashutosh (Reliance Industries Limited) | Dutta, Jayanta (Reliance Industries Limited) | Bhardwaj, Nitin (Reliance Industries Limited) | Gunasekaran, Karthikeyan (Reliance Industries Limited)
Abstract The key objective of this study was to develop a high resolution wellbore stability model for planned highly inclined development wells of an ultra-deepwater field through integrating geological, geophysical, petrophysical and drilling data to design optimized drilling mud weight window. This study describes a customized high resolution wellbore stability modelling process for development wells in ultra-deepwater setting, where shale and sandstone have different pore pressure and stress magnitudes. Un-calibrated and calibrated seismic velocities along with offset well data were used to generate the high resolution pore pressure model for the overburden shale section. Laboratory based geo-mechanical tests, petrophysical logs and offset well events were integrated for the estimation of sub surface stresses and rock mechanical properties for overburden shale and sandstone. Subsequently, separate wellbore stability model was built to estimate the shear failure gradient for overburden shale and sandstone. This study suggests that the mud weight (MW) window in the overburden is primarily governed by two parameters – (i) sand-shale pressure equilibrium state, and (ii) stress anisotropy. The intervals where the sand and shale are not in pressure equilibrium state (i.e. shale pressure > sand pressure), the minimum MW requirement is defined by either pore pressure or shear failure gradient (SFG) of shale formation. Whereas, maximum limit is marked by fracture gradient of relatively less pressured sand formation. Therefore, in such intervals mud weight window becomes much narrower (~1 ppg) than those intervals where sand and shale is in pressure equilibrium (~1.6 ppg). This study also highlights the increase of minimum MW requirement (SFG) in some intervals having relatively higher stress anisotropy. The minimum MW requirement within the main reservoir section having thin intra-reservoir shale is controlled by the SFG of the sand formation, as strength is lower in the reservoir sand than intra-reservoir shale. Results show the importance of high resolution modelling in order to capture pressure uncertainty, thin sands, sand/shale pressure equilibrium state, stress anisotropy and its effects in defining the optimum mud weight window. Based on analysis, further risk zonation was done to highlights intervals prone to wellbore collapse and mud loss. This paper illustrates how the integrated high resolution wellbore stability modeling would help in optimum mud weight planning for highly deviated / horizontal wells to minimize the drilling risks and non-productive time (NPT), especially for challenging field development settings (deepwater, ultra-deepwater, high stress, High pressure High temperature).
- North America > United States > Texas (0.28)
- North America > United States > Gulf of Mexico > Central GOM (0.24)
- Asia > India > Andhra Pradesh > Bay of Bengal (0.16)
- Research Report > New Finding (1.00)
- Research Report > Experimental Study (1.00)
- Geophysics > Borehole Geophysics (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.68)
- Asia > India > Odisha > Bay of Bengal > Mahanadi Basin (0.99)
- Asia > India > Andhra Pradesh > Bay of Bengal > Krishna-Godavari Basin (0.99)
- Well Drilling > Wellbore Design > Wellbore integrity (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
Establishment of Appropriate Normal Compaction Trend NCT: A Critical Aspect for Reducing Uncertainty in 3D Pore Pressure Modelling.
Bhardwaj, Nitin (Reliance Industries Limited, Mumbai, India) | Gunasekaran, Karthikeyan (Reliance Industries Limited, Mumbai, India) | Kumar, Ashutosh (Reliance Industries Limited, Mumbai, India) | Dutta, Jayanta (Reliance Industries Limited, Mumbai, India)
Abstract In 3D Pore Pressure Modelling workflow, establishing appropriate Normal Compaction Trend (NCT) is not only critical but also requires the maximum extent of human interpretation and geological understanding. If not established appropriately, it can introduce substantial uncertainty in the final pore pressure prediction. Though, statistical algorithm techniques are available to establish it, the authors of this paper have demonstrated that establishing NCT manually based on geological logic and regional pressure understanding is much more reliable technique than pure statistical based approach. In this paper, authors utilizes two different approaches in establishing Normal Compaction Trend (NCT) for the study area. First, based on pure statistical technique and second, a manual one based on combination of 3D velocity trends and regional geological pressure understanding. The 3D pore pressure volumes generated from the above two separate NCT’s are then checked for their conformance and agreement with the regional pressure data and understanding, including validation with post drill measured pressure data in the study area. The results and analysis in the study area shows that, establishment of NCT based purely on statistical approach results in higher uncertainty in the 3D pore pressure estimation process. Whereas, manual NCT based on logic results in much more robust, reliable, and regionally consistent 3D pore pressure model with lower uncertainty. In our case study, the average uncertainty in the statistical NCT based 3D Pressures was ranging between 0.8 – 2.3 PPG when compared with actual pressures, while in the case of logic based manual NCT the average uncertainty was less than 1.0 PPG. This case study indicates that in the offshore areas, particularly in areas where there is transition from shelf to slope to deepwater, it is advisable to use all the regional pressure knowledge and geological understanding in establishing the NCT, rather than adopting only the pure statistical methods.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.68)
Origin and distribution of abnormally high pressure in the Mahanadi Basin, east coast of India
Kumar, Ashutosh (Reliance Industries Limited) | Gunasekaran, Karthikeyan (Reliance Industries Limited) | Bhardwaj, Nitin (Reliance Industries Limited) | Dutta, Jayanta (Reliance Industries Limited) | Banerjee, Smita (Reliance Industries Limited)
Abstract Drilling deep wells in the Mahanadi Basin of the east coast of India is highly challenging because of the variations in pore pressure in the Miocene formations. We have observed that the wells drilled in the northern part of the study area have more drilling hazards due to the presence of high pore pressure (modular dynamic test measurements of up to 18.5 ppg) when compared with wells drilled in the southern part of the basin. In the northern part, pore pressure prediction assuming disequilibrium compaction (DC) underpredicts by approximately 2–3.5 ppg when compared with observed pressures; however, in the southern part, pressure prediction matches the observed pressures in the drilled wells. Analysis of sonic velocity-density crossplots suggests that along with DC, some other secondary mechanism also plays an important role in generating excess overpressure in the northern part of the study area; however, the well data do not indicate the presence of an established secondary mechanism, such as fluid expansion, clay conversion, or cementation. The prime difference between the northern and southern areas is the presence of multiple canyon cuts in the northern part and the observation that very high overpressures occur below these canyon cuts. Hence, an attempt was made to ascertain the relationship between the presence of canyon cuts and the observed high pressure with the help of burial history modeling that incorporates the canyon cut features. Pressure estimation based on this approach closely matches the observed pressures in the drilled wells. This very high overpressure observed in the northern part is most likely generated by the combined effect of porosity rebound (due to overburden removal) along with persistence of overpressures that developed prior to erosion. This burial history modeling approach helps in recognizing and understanding the impact of erosional canyon cut events on generation of excess overpressure in the study area. Furthermore, effective stress methods that take secondary pressure generating mechanisms (unloading) into account are used to quantify the difference in pore pressure.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Extensional Tectonics (0.46)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (0.30)
- Oceania > Australia > Western Australia > Carnarvon Basin (0.99)
- Asia > Indonesia > East Kalimantan > Makassar Strait > Kutei Basin (0.99)
- Asia > India > Odisha > Bay of Bengal > Mahanadi Basin (0.99)