Development of formations with stress sensitivity is raising awareness that Geomechanics is a vital aspect of future management. Understanding geomechanical behavior is becoming more and more important for the petroleum industry. It has been reported by many authors (e.g. Herwanger and Koutsableloulis 2011) that, significant changes in pore pressure (ΔP) due to depletion or injection in weak formation might lead to increase in effective stress, compaction, reduction in porosity and permeability, casing deformation, failure and subsidence, challenges in fracturing the formation, closing and opening pre-existing fracture fault re-activation and bedding parallel slippage. The deformations affect the apparent time-shifts from seismic surveys of under- and overburden. The changes in stresses/strain affect the formation of interest as well as the overburden layers and directly affect all operations such as drilling, completion and production strategies because of permeability reduction. Stress affects nearly all petrophysical properties. Compaction, shear casing and well damage, cap-rock integrity, fault reactivation and sand production can occur during Formation depletion. A coupled Finite Element approach is taken for modeling Geomechanical effects induced by production/injection and the cycle dependence between pore fluid flow and def of the tight carbonate, which impact hydrocarbon production. Using Visage, the finite element analysis model for the geomechanical analysis and the fluid flow simulator Eclipse for ΔP determination, this work looks at ΔP – stress coupling, which has significant implications for porosity/permeability reduction. To address these issues, a conceptual two-way coupling model has been constructed using Finite Element method and Eclipse; the results show that, change in pressure has some implications on porosity and pereability. Both 3D and 4D Geomechanical models were developed that describe the state of stresses in the weak formation and overburden as well as changes in stress over time with either production or injection.

No abstract

Mud weight optimization is a key driver in attaining optimum wellbore stability while drilling horizontal wells. This paper demonstrates the role of geomechanical knowledge prior to and while drilling to address wellbore stability related issues to help reduce drilling risk and non-productive time (NPT). To maximize gas production from a tight carbonate reservoir, horizontal drilling and multistage hydraulic fracturing methods have been adopted. For several wells, maintaining wellbore stability has been a challenge without prior geomechanical knowledge of the field resulting in undesired drilling events such as tight hole excessive reaming, stuck pipe, and difficulties while making trips. Even in wells with pre-drill geomechanical analysis for mud weight recommendations, uncertainty in the pore pressure due to depletion along the horizontal section of the wellbore, drilling with one recommended single mud weight (MW) posed great challenge to manage wellbore stability. In this paper, statistical analysis of data is used to investigate root causes of wellbore stability related issues for a number of horizontal wells drilled in the direction of the minimum horizontal stress. The analysis suggests that wells drilled with little understanding of geomechanical properties along the wellbore path encountered significant NPT's compared to those wells where understanding of rock mechanical behavior and in-situ stresses was utilized to make recommendations prior to drilling. In some cases it helped reduce NPT to less than 2% even in exploration wells. Among the successful wells, results from a case study describing the real-time (RT) geomechanics workflow was used to optimize MW enabling drilling the well to the planned target depth. The uncertainty related to pore pressure and intervals of high porosity which creates a significant risk of differential sticking were addressed by incorporating RT data and updating wellbore stability models and providing recommendation to the field operation. The paper demonstrates the role of geomechanics and its impact to drilling operations aimed to reduce operation cost and increase drilling efficiency by eliminating geomechanics-related wellbore stability problems.

Permeability is one of the most important parameters in formation evaluation, reservoir characterization, and hydrocarbon production. There are many methods in the industry to model in-situ permeability, but it is also critical to know that permeability decreases with the increase of effective stress as has been reported in many case studies i.e. permeability is sensitive to changes in stress and pore pressure. In this study, a relationship between permeability, porosity, velocity and effective horizontal stress is developed for carbonate reservoirs using both core and field data. In-situ horizontal stress is related to permeability for several reservoirs around the globe. This paper addresses fundamental controls on stress dependent permeability, as identified through analysis of core samples. The model developed provides a description of effective stress and explains the dynamic impact of geomechanical stresses on key production parameters in an effective way. This will lead to a more robust simulation model and history match for the life of the reservoir. Core plug samples from carbonate formation were tested for conventional measurement (porosity, permeably, and grain density), while acoustic slowness is obtained by wireline and/or LWD measurement to create empirical correlations between permeability, porosity, velocity and effective stress. The correlations show a good agreement with available data that are commonly used in the industry for carbonate. The developed workflow is presented to improve evaluation and enhance the productivity and management of stress-dependent reservoir, also predict sweet spots, optimize completion and predict production that will help in the development of both conventional and unconventional reservoirs.

Published numerical and analytical solutions for wellbore stability predict certain trends in the behavior of hole geometry as a function of time. In general, shear failure is expected to increase in severity with time to produce over-gauged hole sections. However, these solutions do not take into account many aspects of the disturbances produced throughout the drilling process. An investigation of the behavior of hole geometry of a diverse group of wells is conducted to uncover the different relationships between the time-dependent wellbore stability and the related operational practices. The highlighted relationships are then reconciled with published wellbore stability solutions. The disturbances produced throughout the drilling process can include heat transfer between the drilling fluid and the wellbore wall, chemical interactions with the drilling fluid, and mechanical forces working on the wellbore wall. A diverse group of wells in terms of drilling fluid used, drilling practices employed, lithology of formations drilled, and time of exposure experienced is used to highlight the relationships between these disturbances and the time-dependent stability. To aid in illustrating these relationships, the mechanical properties and the stresses are estimated from open-hole wireline logging data. The relationship between time and wellbore stability was observed to reverse from the norm in some cases. It is believed that the anticipated charging of the local pore pressure due to the hydrostatic head overbalance and the heat transfer between the drilling fluid and the formation both combined with different operational practices and drilling events to produce this reversal in the relationship. The drilling events considered include long exposure times due to logging runs and troubles, well control events, lost circulation events, and reaming operations. The observed relationship is then compared with published time-dependent wellbore stability solutions where a form of reconciliation is produced. The presented change in the time-dependency relationships can open new doors for a more sophisticated computational modeling of wellbore stability.