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Geo Pressure


Determination of Regional Stress Magnitudes and Directions: A case study on Offshore Exploratory wells of Tertiary Sequence in Kutch-Saurashtra Basin

GEO India 2018

Excessive wellbore breakouts, wellbore washouts (uncontrolled borehole enlargement) frequent tight pull & held up, undesirable log quality in drilled wells, necessitates understanding the subsurface behaviour of the wells & basic cause of the problems. Rocks at depths are subjected to stresses resulting mainly from the weight of the overlying strata and the locked in stresses of tectonic origin. In-situ stress magnitudes and orientations play a very significant role in understanding the subsurface behaviour during drilling, reservoir modelling, well stimulation and production optimization.

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Geomechanical analysis for feasible CO2 storage in an Indian mature oil field

SPG India

Geomechanical assessment is a very vital step in geological CO2 storage project to minimize the potential risk for CO2 leakage through fracture pathways and fault re-activation caused by CO2 injection. A good monitoring system of geomechanical properties such as in-situ stress, rock stiffness and strength could actually control the potential CO2 leakage pathways. Moreover, a safe and successful storage practive requires wise selection of suitable wells, especially in mature oil field. 

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Issues Faced while Calculating Overburden Gradient and Picking Shale Zones to Predict Pore Pressure

1st EAGE Workshop in Pore Pressure Prediction, Pau, France, Mar 19-21, 2017

Over-pressure is one of the important drilling hazards seen globally. Estimates of over-pressured zones/locations and over-pressure magnitudes have a direct impact on well drilling and completion. Overburden gradient (OBG), Pore pressure (PP) and Fracture Gradient (FG) are the three basic outputs of any pore pressure analysis. OBG is calculated from density (RHOB) log data. As density log data does not start from surface/seabed, we use several equations to compute shallow section pseudo-RHOB and integrate it with LWD/wireline RHOB log data. This article discusses the issues with various ways to fill the data gap of shallow section density. PP is normally predicted against shale zones and then calibrated with the most reliable and direct pressure measurements against sands and log data from adjoining shales. This paper also addresses the various issues faced while picking shale points to predict pore pressure. 

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Analysis of Wellbore Breakouts and Determination of Horizontal Stress Direction from Four Arm Calipers – A Study from Gulf of Kutch, Western Offshore Basin

11th Biennial International Conference & Exposition, Paper ID –37, SPG Jaipur, India, Dec 4-6, 2015

Wellbore instability costs includes billions of dollar per year worldwide because of down hole drilling problems and majority of problems occurring are related to mechanical instability of wellbore. When the stresses exceed the limit of rock strength it fails and if failure is too severe drilling problems occur. It is nearly impossible to drill perfectly gauge hole without any wellbore breakouts, but our aim should be to avoid catastrophic failure and to keep the borehole in the ambit of modest intensity of breakouts and successfully drill the well with limited complications. Each drilled well provides tremendous amount of information about stresses around wellbore. If subsurface Geological and Geophysical data is studied clinically, prevention of catastrophic wellbore failure can be ensured. Breakout data analysis of drilled wells is an important tool in understanding present-day stress conditions in areas where more detailed stress measurements are not available. An understanding of in situ stress conditions is essential to evaluate the potential for slip on existing faults. In petroleum industry, knowledge of borehole stress conditions can be critical in placement of platform and well profile as well as hydraulic-fracturing treatments. The direction of horizontal stresses can be determined with the help of four arm caliper by analyzing borehole ovalisation.

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Uncertainty in Well Log Analyses and Petrophysical Interpretations

11th Biennial International Conference & Exposition, Paper ID –8, SPG India, Dec 4-6, 2015

Petrophysical analysis plays an important role in a reservoir study as it provides primary input data for characterization of subsurface formations and evaluation of resources. Common petrophysical input data to a reservoir study include porosity, water saturation, permeability and mineral or rock volumes. These reservoir variables are typically not directly measured by well logging tools; instead, they are usually derived through multiple processes, including acquisition, processing, interpretation and calibration. As each of these steps involves uncertainty, the resultant petrophysical data will have uncertainty and limitations. Uncertainties from well log and petrophysical interpretations should be analyzed, quantified and explicitly communicated to the integration team in order to be accounted for in reservoir characterization and modeling.

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