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.

Recent activity in developing the heavy oil reserves of the Orinoco belt has required that operators there utilize cutting edge oil field technologies. The latest in pumping technology and horizontal, multi-lateral well completions are being employed and enhanced. Additionally, operators are looking at new approaches to collect and evaluate well and reservoir data. Coiled tubing is also being used to help with some of the well performance issues. To optimize the performance of long, and/or multi-branch horizontal wells, post drilling clean-up is very important. Historically, this issue has often been overlooked or dealt with ineffectively. Not only is this step important for the resulting production performance, an effective system for accomplishing this can have additional benefits for the downstream facilities during start-up. The zones of interest in the Orinoco belt are typically poorly consolidated sands, requiring some form of retaining completion. As slotted liners are most common, an effective method of removing solids from inside the slotted liner may also become a requirement. This paper will discuss the technology of combining concentric coiled tubing with a jet pump to be able to do both the post drilling fluid clean-up and sand removal operations. It will detail the type of equipment used in this application. The paper will also go into specifics of the need for the service in this operation and the corresponding results. Future developments for this technology will also be covered. Introduction Petrozuata C.A. is the operator of a property in Eastern Venezuela's Orinoco belt located just East of San Diego de Cabrutica. This field development is part of a large project incorporating a pipeline network to a 120,000 bopd heavy oil upgrader facility at the coast near Barcelona. Production schedules and targets are all interdependent in order for the project to be a success. Balancing the drilling and completions program with the overall project requirements, the operator has had to adapt the project to cope with the ramping production schedule. Early on, a need to improve well clean-up after drilling was identified. Concerns of potentially reduced well productivity due to extended exposure times (1–6 months) to a well bore storage fluid (WBSF) prompted a need for cleanup prior to the facilities being ready to start production. A relatively new coiled tubing service was employed to address these issues. Previously only implemented in Canada, a system that utilizes concentric coiled tubing with a downhole jet pump was brought in for the clean-up operations. For this well vacuuming system, a 2,500 m (8,200 ft) string of 31.8 mm (1.25") CT inside of 60.3 mm (2.375") CT is used to both, power a specialized jet pump tool and take returns to surface. A program of well cleaning using this technology was implemented and continues to be used to remove the drilling fluid (DIF) and well bore storage fluid (WBSF). Additionally, this process minimizes the fluid processing issues typically faced by the production facility during conventional well clean-up periods. Field History Petrozuata C.A. is a Venezuelan joint venture company that was registered in March 1996 by Conoco Orinoco Inc. and PDVSA (Formerly Maraven S.A.), an affiliate of Petroleos de Venezuela S.A. The Joint Venture has a 35 year operating life and will require the drilling of over 500 horizontal wells that recover 1.5–2 billion barrels of extra heavy oil during that period. Construction activities commenced in January 1997.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe

Although the oil industry seeks to increase the worldwide production of hydrocarbons, various well and reservoir problems can severely reduce oil and gas production from individual wells, leading to the requirement for intervention. For example, in mature fields offshore Brazil, production platforms with minimal open work space and without workover rigs have been a challenge for restoring production in wells with serious scaling problems. The scale build-up reduces production, month by month, until a rig has to be mobilized to replace the production string. Trying to recover production efficiently, service and operating companies have been presenting solutions that circumvent the practical limitations of these locations. In the last three years, an operator's engineering department has worked with service company engineers to develop the means to rig up a 1–3/4-in., 4500-m-long coiled tubing string in a work area of 234 sq. meters and with a crane with a 12-ton maximum capacity. This cooperation allowed intervention in wells on rigless platforms, reducing working time, environmental impacts and costs. These interventions helped to increase oil production from Field A in the Campos Basin and gas production from Field B in the Santos Basin, currently the most important gas field offshore Brazil. Both fields suffer from severe scale deposition -- barium sulfate in Field A and calcium carbonate in field B -- which builds up in the production string and effectively reduces the internal diameter, consequently reducing production. The new successful interventions in these fields using rigless coiled tubing and scale removal techniques enhanced the hydrocarbon production from these fields. In Field A (oil production), interventions were performed in seven (7) wells, providing around a 40% increase in production. In Field B (gas production), interventions were performed in five (5) wells, providing a production increase of around 27% per day. This paper details the planning, logistics and techniques used to successfully meet both challenges. The same solutions would apply in other fields around the world where platform space and scarcity of rigs limit an operator's ability to remediate scale or other wellbore problems that constrain hydrocarbon production. Introduction Market demand has sparked renewed interest in increasing oil and gas production from mature wells in Brazil for the last three years. The result has been an expansion in stimulation techniques using coiled tubing as a thru-tubing tool. Mature production wells, offshore Brazil, are located in both carbonate and sandstone reservoirs. Most of them are naturally depleted and heavy oil / high basic sediment & water (BSW) producers, with a carbonate, sulfate and paraffin scale deposition history. The choice for Coiled Tubing interventions seems to be obvious due to the speed of operation and almost immediate increase in incremental production without production interruption during operations. However, the barriers to project viability included crane lifting capacity, which hindered the ability to place the working reel onboard existing platforms, and the restricted working area available to execute the intervention (Fig.1) in wells ranging from 3500 to 5770 m total depth. Using the correct approach and planning procedures, and involving both service company and operator technical specialists, a new and innovative technique for rigging up and intervention was arrived at to overcome the existing obstacles.

For several years, coiled tubing offshore operations in Brazil have involved the use of nitrogen generation units. Remote locations, lack of liquid nitrogen suppliers and logistical issues, among others, have driven the main oil operator to increase the use of Nitrogen Generation Units. Using a Nitrogen Generation Unit in remote locations, where most of the platforms have very limited space, was the ideal solution for a very old problem of supplying nitrogen. However, when the use of the Nitrogen Generation Unit was combined with coiled tubing operations, another concern arose. In-situ nitrogen generation does not generate pure (99.9%) nitrogen gas. In-situ nitrogen generation can generate nitrogen gas compositions with oxygen contents as high as 5%. Nitrogen with oxygen contents as high as 5%, under downhole conditions of pressure and temperature, can result in severe corrosion problems in the coiled tubing string. Furthermore, together with the increased oxygen content, fluid systems such as completion brines and acids were pumped, which also increased the severity of the corrosive environment. Sometimes operations were stopped because the coiled tubing Bottom Hole Assembly (BHA) was completely plugged by oxidized/corroded metal solid flakes or the coiled tubing string became so corroded that it required inspection before further use in job operations. Based on these corrosion and safety issues the use of in-situ nitrogen generation loses its benefits. To find a solution to this corrosion problem, a laboratory research study was performed with the most commonly used coiled tubing string material and the pumped treatment fluids under surface and downhole conditions with the maximum percentage of oxygen concentration that could be expected in operations. Several corrosion inhibitors and mixtures were tested for their ability to control the corrosion of the coiled tubing string. After laboratory testing established which inhibitor systems would control the corrosion rate of the coiled tubing, yard tests were performed to confirm that the inhibitor would work in the field. After the field trial was performed successfully with several applications, the recommended practices were adopted from this research to avoid the corrosion problem faced in the past with the use of offshore nitrogen generation units. This paper presents the sequence of events of this project: the coiled tubing corrosion observed in the laboratory research studies, the performed yard trials; the recommended field applications, as well as the benefits that this study and final application brought to the operations.