The success of a scale inhibitor treatment depends on placement efficiency. The scale inhibitor should be placed so that all water-producing intervals accept a sufficient quantity of the total treatment volume. If significant permeability or pressure variations are present in the interval to be treated, treatment fluid will enter the zones with the higher permeability and lower pressure, leaving little fluid to treat the other zones, which can be the water- producing zones. The challenge is even greater in long, horizontal wells with significant permeability and pressure contrast.
To achieve a more uniform fluid coverage, the original flow distribution across intervals often needs to be altered. The methods used to alter this are called "diversion" methods. The purpose is to divert the flow from one portion of the interval to another. In response to this challenge, a joint study with the objective of improving the placement of treatment fluids was initiated by a major operator in the North Sea and two service companies in 2002.
The joint work resulted in development of a fully viscosified scale inhibitor system. The system comprises a purified xanthan viscosifying agent, a standard scale inhibitor for downhole scale squeezing, and a breaker to achieve controlled gel breaking down hole.
The system has been field tested at Norne field in two long horizontal wells and at Heidrun field in one long deviated well, all with significant permeability variations and crossflow. The operations were successful and the scale treatments have protected the wells from scaling. This paper describes the product qualification process, placement simulation, temperature prediction, gel breaking characteristics, case histories, and post-job evaluation.