Ultralightweight and Gas Migration Slurries: An Excellent Solution for Gas Wells

Abstract

Abstract This paper shows the excellent results obtained using ultra lightweight and gas migration slurries (ULWGMS) on wells of San Joaquin and Santa Rosa fields, located in Anaco City, Eastern Venezuela. There are several gas fields in Anaco area, with complex wells, due to their low frac gradients, pressurized water zones, depressurized gas zones, H2S and CO2 content, clay sands, and, in some cases, presence of micro fractures. These sands are also bounded by interbedded shales, with trapped gas and water, experiencing larges amount of losses of mineral oil mud, during drilling. All these characteristics contributed to unsuccessful primary cement jobs in the past, attributed to inappropriate slurry designs, with unsuitable properties to deal with all the above factors. Statistics showed that 2 out of 3 wells in this field failed due lost circulation issues, requiring remedial cementing to address gas control, and water migration. Ultra lightweight slurries were conceived, with adequate mechanical properties (flexible and tension strengths), in addition to providing H2S and CO2 resistance. The first 9.2 ppg ultra lightweight slurry was first used in 2003 in San Joaquin field, and indicated good isolation, by logs runned. Subsequently, ultra lightweight slurries with densities from 9 to 11 ppg have been applied in 18 different wells in Anaco area, showing excellent zone isolation results, demonstrated by low water cut, and good bond logs.