Field Development and Production Optimization Integrating Reservoir Compaction, Sand Production and Wellbore Stability Modeling: A Field Case Study
Authors: Alcalde Osmar Rene , Ozan Cem , Jimenez Malpica Gerardo , Perez Suarez Luis Alejandro , Alvarellos Jose , Magee Marian , Ewerton Araujo 
Published: March 2015

Some technical uncertainties during the planning phase of field development can be identified and properly addressed with the aid of a suitable geomechanical analysis. Uncertainties includes unrealistic mud-weight drilling windows (with NPT related to WBS), pressure drawdown uncertainties related to sand production with wrong selection of wells and perforations orientations and uncertainties in subsidence and production loss as a result of reservoir compaction. Operators have been faced with some of the above concerns during the development of a field.

This paper presents a workflow of how an adequate elasto-plastic end-cap rock material model and the understanding of local stress regime (along with field data calibration), helps to integrate wellbore stability (WBS), sand-free production predictions (with optimal oriented perforations) and reservoir compaction for production optimization and field development.

A material model (elasto-plastic stress-strain relationship) describing the strain-hardening behavior of the rock was implemented for better characterization of the sand production phenomena. Also, to simulate reservoir compaction in a more realistic manner, a modified Drucker-Prager end-cap compaction model was developed. The implemented models were calibrated with laboratory, drill-steam test and wireline data. The study includes design and analysis of triaxial, hydrostatic compressive and TWC laboratory tests from offset wells.

The results show that a more precise constrain on the present stress regime was achieved, thus providing an optimal drilling window that could not be predicted before in the area (i.e, enabling horizontal drilling). From the sand-free production point of view, horizontal cased wells are limited to be drilled in a W-E azimuth with vertically oriented perforations (for 500 psi reservoir depletion and drawdown less than 700 psi). For a pressure depletion of 20 Mpa, reservoir compaction generates up to 5% to 10% porosity reduction with a subsidence of 1.8 m (2.1 m compaction at the reservoir structure top). This compaction could generate loss permeability from 30–50%. The results helped the operator to make decisions regarding planning of field development; for instance, open hole gravel pack completions for horizontal wells in the N-S direction are not an option for field development. Horizontal wells need to be cased and drilled in the SHmax direction.

Introduction

During the planning phase of field development it becomes necessary to identify technical uncertainties and properly evaluate them, so that unexpected costs can be reduced or avoided. Some of the questions related to these uncertainties are: is the most favorable perforation orientation free of sand in accordance with the most stable wellbore trajectories to drill? If yes/not, is cased hole or open hole the best completion option for a given pressure drawdown? How significant is the compaction effect on production throughout the structure of the reservoir?