Flint R. George

Orienting Live Well Perforating Technique Provides Innovative Sand Control Method in the North Sea

The Varg field is a development in the North Sea operated by Saga Petroleum. It consists of a not-normally-manned wellhead platform (WHP) with dry wellheads and a floating production storage offloading (FPSO) vessel for processing the crude. The reservoir is heterogeneous sandstone of Upper Jurassic age, with estimated reserves of approximately 35 million stock-tank barrels. During development planning of the field, it was felt that sand production was likely to occur, and this phenomenon was actually experienced during well testing. Since this development was considered to be a marginal field, an extensive program was initiated to review and select a technical completion solution that would minimize the risk of sand production so that production potentials could be maximized. This paper will discuss how a unique perforating solution was developed to provide the controls needed to manage the potential for sand production. The first part of this paper will summarize: 1) the drainage strategy and implications of this strategy on selecting the perforation intervals, and 2) results of a rock mechanics study that focused on the conditions critical for the onset of sand production as well as recommendations for minimizing the risk. The primary recommendations were to avoid perforation of the weakest intervals and to shoot perforations that would be oriented parallel to the maximum horizontal stress. The second part of the paper will describe how successful oriented perforating was achieved in these wells. The primary completion challenges included the following: 1. Development of a slickline system that could perforate the entire zone simultaneously in a given direction in a vertical well. 2. A means to remove the perforating guns from the well without having to kill it after completion of the perforation as there was insufficient rathole to leave the guns in the hole. An oriented modular perforating system was developed so that the above conditions could be achieved. The requirements were met by installing a gun anchor in the well before the completion was installed. Then, the orientation of an orienting lug was measured with a gyro, and based on the data from the survey, the guns were aligned in the correct orientation. Subsequently, gun sections of length maximized to available lubricator length were run on slickline. The gun section aligned itself automatically to the measured orientation of the orienting lug because of the equipment design. Currently, three wells have been perforated using this system, and the desired results have been obtained.