New Approach for Optimizing Cement Design To Eliminate Microannulus in Steam Injection Well

Over the past few years, several papers have been published discussing the long-term mechanical durability of the cement sheath in steam injection well. Looking at this, the research is continued to find the right process flow in optimizing cement design as a new approach to eliminate microannulus in steam injection well. This process flow is based on previous experiences cementing in steam well. Duri Steam Flood is located in Sumatra, Indonesia was taken as a case study in this research. As we known, changes in downhole stress conditions that occur during the life of a steam injection well are extreme. The stresses in the cement sheath induced by the extreme temperature cycling could result in severe mechanical damage and ultimate failure of the cement sheath, potentially leading to microannulus.

From well life analysis, the result found that the steam well in Duri Steam Flood has 6% risk of cement sheath failure in less than 5 year. Because of this, the research is carried out to find the reason and solution of this failure. Firstly cemented annulus stress simulation is proposed to verify this cement sheath condition. Expanding cement is one of the proposed solutions in this study based on simulation recommendation. The behavior of the cement sheath with recently developed annulus and linear experiment is proposed. Three parts of testing for linear expanding test were conducted. Firstly, test at bottom hole static condition temperature (120 degF) and pressure (1000 psi) curing for 30 days. Then, test at bottom hole static temperature condition curing for 2 days with variation of pressure (1000 psi to 3000 psi) and test at bottom hole static pressure condition curing for 2 days with variation of temperature (100 degF to 300 degF). Magnesium Oxide (MgO) is used as an expansion additive with conventional cement slurry (Class G and 35% BWOC Silica). The concentration used is 2.7% BWOC to 7.0% BWOC. Finally compressive strength tested at bottom hole static pressure with variation of temperature (150 degF to 280 degF) at 24 hours. Therefore, a process guideline is finalized based on last cementing experiences, experiment results and cost analysis to find the most optimize cement slurry in steam injection well.

Introduction

Cementing is a part of well completion process before the well is ready for production for oil or gas from reservoir. It is very important process to make sure the cement job has to fulfill multiple conditions, but its main function is to prevent fluid and gas flow through the annulus by ensuring an impermeable bond and exhibiting sufficient compressive and shear bond strength. The sealing can be affected by various factors: poor mud removal, bad slurry properties and borehole conditions (expose to the change in temperature and pressure as always happen in steam injection well). It is also recognized that the volumetric changes of cement during hydration substantially contribute to these problems.