The US Gulf of Mexico is one of the few regions in the world where wells are completed in the deepwater Miocene and Lower Tertiary reservoirs. These deepwater plays have required constant technological improvement to equipment service capabilities in order to maintain integrity in the 30,000-psi environments and minimize risks. Although capable tools and guns have been developed, continuous assessment of reliability still remains vital in the exploratory processes.Testing for production analysis in deep and ultra-deep water is critical, and when target reservoirs produce heavy oil, gas and condensate, or are in HP/HT environments, planning safe tests with risk mitigation that can gather high-quality data is paramount. Because of the high rig rates for deep-water operations, prolonged periods of low temperature and heat loss that can affect production or enable hydrate formation and other environmental challenges cannot be ignored. Fluid volumes and water depths can increase well-control time and expense. Also, since well tests are conducted from mobile vessels, alarm and subsea equipment philosophies are critical to success, and well-test string configurations must be flexible yet control well safety.Obviously, all issues must be understood for the program plan to anticipate the potential challenges. The purpose of this paper is to explore these issues as well as discuss mitigation methodologies. The considerations, merits, and limitations of various solutions will be considered. Lessons learned from actual cases will compare the consequences of inadequate preparation to the benefits of proper design. This paper explains why and how the methods and equipment suggested should be used and will include: 1. DP vessel testing 2. Well integrity at extreme depths and pressures 3. Functional pressure-operated tool windows 4. Coiled tubing 5. Cushion and mud-type criteria 6. Hydrate prevention 7. Perforating strategies.
The main focus of any perforation system is to establish effective hydraulic communication between the wellbore and the reservoir. A primary attribute for this connection is maximum penetration in the undamaged reservoir rock, especially in mature and highly depleted reservoirs. Drilling and completion fluids cause a certain amount of damage in the near well bore region, the perforating tunnels must bypass the damaged region to create the effective flow path and enable maximum well productivity. The challenge is to create a deep, clean, undamaged tunnel to maximize oil and gas production from the reservoir. A new Triple-Jet™ perforating system was recently introduced in the North Sea, and it uses the existing shaped charges and a slightly-modified hollow steel carrier as from those currently used in the industry. This system provides a new perforating concept that exploits the beneficial aspects of firing a bank of three co-linear focused charges into the formation. The jets from the upper and lower perforating charges are angled to intersect within the formation, while the jet from the center charge is slightly delayed such that its perforating tunnel has the benefit of penetrating the tensile-stress-altered rock within the formation. The resulting shock wave from the converging jets produces a proportionally smaller crushed zone and weakened material around the perforation tunnel that is easily removed by low underbalance methods. Simulated downhole testing conditions show that this system significantly improves both penetration and flow performance and provides potentially greater well productivity than the same charges loaded in a traditional hollow steel carrier with similar charge-to- charge phasing angle. Because the Triple-Jet system produces weakened rock that is easily removed by low underbalance, it is ideal for both new well completions and re-perforating existing wells. The new perforating technology complies with similar safety standards as conventional perforating systems, raises no additional issues with explosives licensing, guns are run and fired in the conventional manner, and does not require substantial new work or training for the crew or platform management. This paper compiles a series of laboratory experiments that are modeled with an analytical simulator and provides a brief description of the job-field application.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe technology for coiled-tubing-conveyed perforating (CTCP) under extreme conditions has been available for a number of years, but until recently, the techniques have not been used in Venezuela. This paper will describe the first experiences in which CTCP has been used in this area.The first candidate identified for the application was a new well in East Venezuela. This well was the first high pressure, high temperature (HP/HT) highly deviated deep monobore well completed in El Furrial Field in the North Monagas area that was perforated underbalanced with this technology. Although several traditional perforating methods were initially evaluated, the decision was made to perform the operation underbalanced using rig-assisted coiled-tubing technology because of the following advantages that could be realized from use of this method:• Debris in the tunnel would be reduced, minimizing the potential for formation damage. • The debris could be circulated out more easily.• The use of kill fluid to control the well would not be necessary. • By eliminating the cost of the kill fluid and the resulting costs of handling the returned kill fluid, well costs would be reduced. The operation was performed in a live well with a 77degree maximum well deviation and total depth (TD) of 17,907 feet. Several engineering simulations were performed before the job. These simulations enabled the operator and service engineering personnel to quantify the effects of CT fatigue, lockup, stresses, forces, elongation due to weight and temperature, and buoyancy effects. Other important factors considered were safety, health, environment, quality and well control, taking into account all possible contingencies. Finally, nine (9) coiled tubing runs were performed to complete the well, a total of 1,190 ft of 3 3/8-in., 6 shots per foot (SPF) and 2 ¾-in., 6 SPF guns were run. In all of the coiled-tubingconveyed perforating runs, the expended guns were retrieved successfully under live well conditions. To retrieve the guns without killing the well, a subsurface flapper-type safety valve, which enabled the operations to be performed under controlled conditions, was used.Currently, the well is producing 19,621 BOPD through a 1-in. choke and 1,591 psi surface pressure.Production and wellhead pressure expectations for this well were exceeded.
As development of hydrocarbon reserves continues to move into deeper and more complex reservoir conditions, operators have found that conventional techniques for testing, perforating, and stimulating have not been capable of providing satisfactory results in the severe well conditions. Even if operationally satisfactory, they have been unable to meet the goals for cost efficiency. This paper describes an experience in the Tropical Field, located in eastern Venezuela and operated by Repsol - YPF in which the reservoir is characterized by high-pressure reservoirs and complex geology due to faults and high-dip-angle formations. Repsol needed a method that would optimize well testing operations, improve safety, and cut costs without compromising the results of the operation; thus, a major change to traditional drill stem testing operations was needed. A technique, which would eliminate the need to kill the well to retrieve the guns and also provide the flexibility to test, evaluate, and fracture the well, was suggested. Instead of using a drilling rig or a work-over unit as in the standard drill- stem testing operation, the procedure would allow the operator to perform a rigless well test evaluation using optimum underbalanced conditions in favor of the reservoir. Several alternatives were evaluated for perforating and testing the well. After thorough examination of all possibilities, snubbing- and coiled-tubing-conveyed perforating (CTCP) methods were selected as the most promising alternatives for achieving the objectives proposed at the beginning of the project. While coiled tubing had been used to perforate in other areas in Venezuela, coiled tubing combined with snubbing had not been used in Venezuela. This paper will focus on the methods developed to satisfy the operational challenges, the results obtained with the use of the newly applied technologies, and how the technology was able to address the operator's needs as well as the difficult reservoir conditions. Instrumental in the success of the methodology was the combined use of super-deep penetration technology, state-of-the-art memory tools for depth correlation, real time data transmission, and the flexibility to perform several operations during a rigless well-test evaluation. This case history represents the first live-well intervention using snubbing and coiled-tubing perforating techniques performed successfully in eastern Venezuela. Introduction The Tropical Field is located in east Venezuela approximately 28 miles from Maturin, capitol of Monagas state, in the North Monagas Area. This location is one of the most prolific production areas in the country. The reservoir is characterized by high-pressure and complex geology due to faults and high-dip-angle formations. The field is presently under development, and 4 wells have been drilled. Oil is produced from two locations - the San Juan Formation at approximately 13,890 feet and from the San Antonio Formation at approximately 14870 feet. The average total depths in the wells are 15,800 ft. and are slightly deviated. Thus, perforation techniques had to be capable of operating in complex geology due to faults and high-dip-angle formations. Perforating Techniques used on Tropical Area. During the exploratory stage of field development, tubing-conveyed perforating (TCP) was used since it offered the capability to perforate the well in an underbalanced condition. In the first wells, the TCP string included the DST string for evaluation. The wells still had to be killed, but underbalance was obtained. Then, rigless perforating systems were considered. The objective of this change was to optimize the cost involved during the well-testing evaluation operation, and at the same time, obtain the benefits that can be achieved from having the completion already in place and the capability to perforate without killing the well. The technology applied at the beginning of the project was to perform TCP on coiled tubing; however in the well discussed in this case history, it also became necessary to use a snubbing unit to perform the gun runs because of the difficulties experienced in meeting operational requirements in the complex geology.
The effective combination of propellants to generate a high-pressure pulse to create micro fractures has been proven to be successful in a number of wells in Ecuador.Recently, the inclusion of surge chambers in the bottom hole assembly has been proven to provide improved cleanup of the perforation tunnels created by jet perforators. This minimum surge pressure across the formation results in a dynamic underbalance that improves well productivity. Owing to the improved cleanup, there is a better path between the reservoir and the wellbore, which has demonstrated a more than 50% increase in well productivity. The ability to delay the opening of the chambers after gun detonation is critical in creating a dynamic surge from reservoir to wellbore, thus enhancing the dynamic flow and removal of fluids and solids from the perforation tunnels.This combination of overbalance and dynamic-underbalance immediately after perforating has also provided a method for cleaning perforation tunnels, even when perforating overbalanced with wireline-conveyed guns.This technique has been highly successful in the East Basin of Ecuador, especially now that near-wellbore stimulation techniques to clean the perforation tunnels can be achieved with wireline-conveyed guns instead of using a rig to provide tubing-conveyed perforating (TCP) services to create optimum conditions during perforating. This combination of techniques provides an effective solution at a reasonable cost that optimizes reservoir connectivity with the wellbore, significantly increasing the productivity index.However, for these techniques to be used successfully and create the necessary conditions to remove debris damage from the perforation tunnels, it is imperative that the software models and simulations be provided by experienced and well-trained engineers.Prior to the job, the service is modeled using state-of-the-art software simulators to predict the dynamic forces acting on the wellbore. When the job is executed, fast-gauge memory recorders are used to capture the pressure and temperature data at the time of the perforation event to validate the modeling. This technology has demonstrated great success in Ecuador by improving well productivity by as much as 50% when compared to other nearby wells in the field.
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