Sand production is a well-known and costly problem in shallow unconsolidated sands. For years slotted liners have been used to control sand in these types of reservoirs. However, over time sand, fines and other debris can clog slots or make their way into the liner itself, thus blocking production. A new live-well intervention technique making use of a concentric coiled tubing (CCT) vacuum tool (VT) has been implemented in Venezuela1,2,3. The technique incorporates a venturi jet pump mounted on CCT, and is specifically designed to remove solids and/or fluids from the wellbore without placing hydrostatic loads on the reservoir. In sand vacuum mode, strong jets fluidize and mobilize solids into the vacuum as well as prevent a stuck pipe scenario. The jets also aid in opening clogged slots by loosening fines that may be blocking flow. When the VT applies suction, a localised pressure-influenced-zone is formed in the very near wellbore - thus providing an isolated "point-load" drawdown on the formation.
The jetting action combined with point-load drawdown and drag forces results in solids removal from behind pipe as well as inside pipe. Evidence of this phenomenon are jobs where a solids volume greater than the entire liner has been retrieved to surface. Post job results on jobs performed in Venezuela consistently show reduced skin, increased Productivity Index (PI) and higher long-term oil production.
This paper describes the latest in CCT vacuum technology as well as it improvement in time via case studies of several different applications in Venezuela. Also discussed are simple lab techniques, which reveal serious completion issues such as liner slot erosion, fines invasion and drilling fluid damage.
Introduction
Venezuela is home to a vast array of oil and gas reservoirs, and is currently 6th. in the world, in terms of oil reserves. Western Venezuela is dominated by medium to heavy oil in and around the Lake Maracaibo area, while Eastern Venezuela contains large gas deposits, light oil and the world's largest heavy oil deposit. In the West a significant portion of medium to heavy oil production comes from Miocene to Eocene sands of fair to poor consolidation that require a slotted liner for sand control. Some of the specific fields making use of this completion are; Boscan, Mara, Tia Juana, Lagunillas, Bachaquero and Mene Grande, which wrap around Lake Maracaibo. In Eastern Venezuela slotted liners are used almost exclusively in the four major heavy oil fields of the Orinoco Belt (Machete, Zuata, Hamaca and Cerro Negro). These reservoirs are shallow (2,000 to 5,000 feet) and the pay sands are generally very poorly consolidated. It was thought that horizontal drilling in these sands would be impossible, but advances in muds and drilling practices spurred a massive investment and now thousands of wells have been completed with non gravel packed, horizontal, slotted liners. Slotted liners have been popular because they are easy to run and are cost effective.
