Rigless Water Shut-off Experience in Offshore Saudi Arabia

Abstract

Abstract As the offshore Saudi Arabia fields mature, more wells are becoming wet and consequently more wells are dying due to water encroachment. These dead wells and associated facilities are valuable assets that need to be effectively utilized throughout the producing life of the fields. Therefore, remedial actions to revive dead wells are vital strategies to maximize revenues. Rigless water shut-off techniques in conventional wells have been successful due to relatively simple wireline interventions. However, water shut-off jobs in horizontal wells are more complicated and are more challenging tasks for oil companies, including Saudi Aramco, due to their associated high cost and cement placement uncertainties. This paper is a study of six years of rigless water shut-off efforts to revive dead wells in Saudi Aramco's Northern Area offshore fields to extend the producing life of the wells and enhance oil recovery. During the study period, 46 rigless water shut-off jobs were executed with a 91% success rate. Of the 46 water shut-off jobs, three jobs were successfully implemented on dead horizontal cased hole wells using coiled tubing (CT). The job success is attributed to proper problem diagnosis, job design and execution, resulting in a significant production gain and workover cost avoidance. Introduction The majority of the water shut-off jobs covered by this study were conducted in wells completed in sandstone reservoirs. A typical Saudi Aramco offshore reservoir consists of a ± 200 ft Main Sand underlain by a strong water aquifer, which supplies the pressure support. Sand Stringers are usually separated from the Main Sand by an impermeable shale break (see Figure 1). Normally, a well is completed in the Main Sand. Once the producing zone is watered out, a Pulsed Neutron Log (PNL) is required to identify the water movement as well as the remaining pay zones to properly conduct a remedial action to restore well productivity. In general, the most common type of downhole water encroachment seen in Saudi Aramco offshore fields is bottom water movement. In this case, the oil-water contact moves up slowly with time, due to a strong aquifer drive, until producing zones are swept. One common water shut-off technique to re-activate dead wells due to excessive water production, is the use of a mechanical solution to permanently abandon bottom watered out zones in order to produce upper dry zones. The objectives of this paper are toprovide an overview of six years of rigless water shut-off efforts to revive dead wells in Saudi Aramco's Northern Area offshore fields using Mechanical Through Tubing Bridge Plugs (MTTBP's) andshare our experience on the first successful attempts in Saudi Aramco to conduct water shut-off jobs on three dead cased hole horizontal wells (two wells were re-activated using MTTBP's and the third well using the cement and gel plug technique). Water Shut-off Evaluation In Saudi Aramco's Northern Area offshore fields, a total of 1,045 oil producers exist. Of these, 544 (52%) are producing wet. As the number of wet wells continues to increase, more effective downhole water management practices are needed to control produced water. Prior to any water shut-off job to restore productivity of dead wells due to high water cut, a PNL is run to identify the type of water movement and remaining pay zones for re-completion potential. Once the type of water movement is clearly identified, the well completion is reviewed (tubing size, tubing depth location with respect to pay zones and production casing size) to determine the most appropriate water shut-off technique.