Prediction of the critical drawdown for poorly consolidated rocks

UDK: 622.276.031
DOI: 10.24887/0028-2448-2021-7-82-85
Key words: poorly consolidated reservoir rock, rock mechanics, stress-strain state (SSS), strength, critical drawdown
Authors: S.V. Zhigulskiy (Gazpromneft NTC LLC, RF, Saint-Petersburg; Sсhmidt Institute of Physics of the Earth of the RAS, RF, Moscow), A.S. Gunkin (Saint-Petersburg Mining University, Saint-Petersburg), A.V. Khitrenko (Gazprom Neft PJSC, RF, Saint-Petersburg; Gubkin University of oil and gas, Gazprom Neft)

Poorly consolidated reservoir development process is followed by complications that are related to sand production. The development of such reservoir requires strict control over the rock failure of the bottomhole zone. Rock failure at the bottom of a well occurs due to the reason of the irreversible deformation occurrence. Consequently, reservoir rock loses its integrity due to the influence of critical stress level. Thereby, one of the main aims of geomechanical modeling is the evaluation of the well critical drawdown with the aim of prevention of the sand production and assurance of the borehole wall stability. This paper provides a detailed description of the critical drawdown evaluation tool. The evaluation was performed by two methods. In the case of a simplified criterion, it is possible to obtain a continuous drawdown profile in a well of a given orientation, while a full-fledged criterion at a given drawdown is used to estimate the rock failure zone. The current approach was implemented in Python programming language that allows to quickly and efficiently carry out calculations for a group of wells simultaneously. Evaluation of stress-strain state was performed for both initial reservoir conditions and preassigned time step for the reservoir pressure. Thus, for a well of any orientation, based on data from one-dimensional geomechanical modeling, the critical drawdown is calculated for two variations of strength criteria, taking into account changes in reservoir pressure. The demonstrated approach allowed to obtain the critical drawdown profile in the well considering the change in reservoir pressure. Calculations were carried out for several wells, and appropriate recommendations were formed on the bottomhole pressure for a given period of well production.


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