Gas Migration After Cementing Greatly Reduced

Abstract

Abstract Gas migration through cement columns has been an industry problem for many years. The most problematic areas in Saudi Aramco operations for gas migration are in deep gas wells (Khuff / pre-Khuff) in the Ghawar field. Gas migration in deep gas wells occurs when drilling through the base of Jilh dolomite. To control gas influx, cement densities required to successfully cement this zone could be as high as 170 pcf. Specially designed cements were used to "zone isolate" the high pressure coming from the formation. High density/low fluid loss cements were used in the past with limited success. More recently, Liquid Latex in combination with expanding additives have been used to help reduce the gas flow potential before and after the cement sets. The objective of this study was to develop effective cement formulations to control deep gas migration during primary cementing and optimizing costs of expensive cement additives. Three major physical properties lab equipments were utilized for this study. First, a cement gas migration system (CGMS) was utilized to measure gas flow through a cement column prior to the setting of the cement. Second, the static gel strength analyzer (SGSA) was used to determine the static gel strength of well cements to confirm the data from the CGMS. Third, the American Petroleum Institute (API) expansion cell was used to determine the expansion properties of set cements. Data from the CGMS, SGSA and API expansion cell was successfully utilized to greatly reduce the gas migration problem. The consumption of expensive cement additives (latex and expansion) in the cement formulations were optimized for cementing gas wells with success. The in-house cement design optimization saved the company as much as 59% on the cost of obtaining the desired cement fluid properties.