Drilling Severely Depleted Sands in the Gulf of Mexico: The Benefits of Cloud Point Glycols

Abstract As mature hydrocarbon reservoirs become more depleted, drilling through depleted sands is becoming increasingly common. High levels of overbalance increase the risk of occurrence of lost circulation and / or differential sticking. Recently, three Gulf of Mexico wells successfully drilled through depleted sands with overbalances ranging from 3500 to 4600 psi In each application, a glycol-enhanced water-based mud (WBM) was used. In this paper, the formulation and application of this specially formulated WBM are discussed and the results documented. The use of glycols as additives in WBM has been increasingly common in the past several years. Work has focused on certain glycols that exhibit "cloud point" behavior. Although soluble at surface temperatures, under the correct downhole temperatures, these glycols become insoluble and form an emulsion. Dynamic filtration and lubricity data from the laboratory, coupled with field performance from the Gulf of Mexico wells indicate enhanced filtration properties. A theory for understanding the phenomenon in WBM is offered, one which exhibits many similarities to the performance of oil-based and synthetic based muds