Abstract
Steamflooding is an emerging technology to enhance the production of heavy oil from various geological formations. A pilot study to test the steam-enhanced production has been conducted in a Middle Eastern oilfield for several years. Anhydrite (CaSO4) is one of the dominant scales during steamflooding and scale control has been included in the program. In this paper, a case history of laboratory scale inhibitor testing and field implementation will be discussed. A total of over 120 chemicals including phosphonates and polymers obtained from various chemical and service companies were tested. Only a handful of inhibitors passed the initial screening and were selected for thermal stability and brine compatibility testing. The critical limit of saturation index (SI) where a scale inhibitor can be effectively used to control scale is established to be about SI = 0.89. Above this value, a high inhibitor dosage is needed to control scale. Based on detailed laboratory tests, two inhibitors, one sulfonated polycarboxylate and the other one phosphonate and carboxylic acid, were recommended for field application and one of them has been applied in the production through continuous injection to prevent anhydrite scale formation. The successful anhydrite scale control with the recommended inhibitor proves that the protocol we have developed is valid and effective.
Introduction
Steamflooding, also known as continuous steam injection or steam drive, is an emerging technology to enhance the production of heavy oil from various geological formations. During a steam flood, steam generated at the surface is injected into the reservoir through specially distributed injection wells. Injected steam, when entering the reservoir, will heat up the crude oil and thus reduce its viscosity. Also, the steam, as well as the water that condenses from the steam, can generate an artificial drive that sweeps oil toward producing wells. Other advantages in enhancing oil recovery can also be found within steamflooding, for example, distilling light component of the crude oil and enhancing near-wellbore cleanup.1
