Effective elimination of unwanted solids from the production stream is a key element of production optimization, and one that requires an engineered approach.

PetSec Energy Inc., a large, growing independent in the Gulf of Mexico, recently developed three monobore wells in its West Cameron 352 field offshore Louisiana. This mature field with existing completions also contains newly drilled secondary targets primarily consisting of high permeability gas formations. Hydrocarbons in this field are located in fault trap reservoirs and are pressurized and produced by a water-drive mechanism.

The challenge was to develop a cost-effective well system compatible with multiple, high-rate, sand-controlled completions for stacked pay intervals. Since the three prospects had limited reserve potential, conventional drilling and completion methods would not be feasible. At the same time, any rigless completion method ultimately selected would have to be economical compared to current rig rates. It would also need to involve minimal mechanical risk and maintain the best practices developed for sand-control completions in the area. A new service from Halliburton called Crimson Vent Screen (VS) was chosen.

This service was developed to make bypassed reserves economically viable by matching the proper vent screen assembly design, conveyance mechanism and sand-control method with overall project coordination. As a total engineered rigless solution, the service would be able to withstand the maximum anticipated production rates which were determined through an advanced modeling system that incorporates the well parameters and well deliverability to determine vent screen completion stability.

Traditional sand control

Vent screen or dual screen technology was introduced in the late 1980s and is now a commonly accepted completion strategy. Vent screen assemblies consist of a primary production screen long enough to cover the perforations, a length of blank spacer pipe, and a short upper section of screen bull plugged on top. Using vent screens allows subsequent completions of payzones up hole to be performed more cheaply since no production tubing has to be removed to run additional sand control assemblies. Additionally, predicting and modeling vent screen completions through correlations and simulators developed in both field experience and laboratory experiments have increased the success rate of vent screen completions to a level equivalent to other sand control/stimulation treatment strategies.

The technique typically employs two screen assemblies separated by blank pipes that are placed and packed in casing. The screen and blank assembly are then run into the hole through the production tubing, using electric line, slickline, or coiled tubing and are set on bottom. Following that, the sand control treatment, consisting of a gravel pack or high-rate water pack, is emplaced at the desired rate. At the end of the treatment, proppant is allowed to pack into the screen and the blank annulus. Production enters the lower screen section and exits the upper screen section. This method is traditionally applied only to low-reserve, cost-sensitive reservoirs, or as a last-ditch effort to control sand and production in old wells.

A new chapter in sand control

Crimson VS completion service uses recent innovations in coiled-tubing and sand-control technologies to enable rigless through-tubing vent screen sand-control completions for both initial and alternative remedial completions. The service combines Antifluidization (AF) screen technology, real-time coiled tubing depth-measurement tools, and advanced proppant delivery systems. The results increase the operating envelope for vent screen through-tubing sand control technology, allowing wells to produce at rates higher than 50 MMcf/d of gas or 10,000 b/d of oil. Typical through-tubing completion candidates are identified as gas wells with three to five BCF of reserves, stacked pays, high rig costs, and intervals with six to 12-month productive life in each zone.

The heart of the service is an engineering design that selects the right fluid system, blank design and proppant coating. To reduce costs and project time, this deployment system is tailored for each well. The job is designed using proprietary algorithms developed to predict the maximum flow rates that are attainable through a given vent screen completion geometry. The mathematical models help to predict the production rate at which the vent screen annular pack will fluidize or fail.

After determining the failure point, the completion engineer is able to increase the fluidization point by utilizing VentPac AF coating and treatment design. This patented proppant coating system has enabled achievement of the highest rate of vent screen completions in the world to date. A pressure deployment technique of lubricating vent screens under pressure using a specialized plug has also been developed. This method is safer than using the subsurface safety valve as a pressure barrier. By utilizing the pressure deployment system, the risk of a blowout during screen deployment is reduced significantly.

These innovations can improve reserve recovery rates and completion efficiencies; reduce mechanical risk, and completion costs while extending the economic life of the well and controlling fines migration.

Track record

To date, the completion systems have been deployed in casing sizes from 31/2-in. monobores to 93/8 in. casing and in production tubing sizes from 23/8 in. to 41/2 in. In addition, the system can be deployed as a single trip system for most well geometries, further decreasing job costs, reducing exposure hours for personnel, and improving well control.

Most importantly, the lower completion costs allow operators to pursue and produce reserves that in the past would have been considered uneconomical and would be eventually bypassed. The system also vastly improves the longevity of the vent screen completion method and has extended the typical operating range from an average life span of a few months to more than 24 months. These improvements allow operators to utilize the service on candidates with larger reserves per zone and have produced significant cost savings by eliminating the need for a rig to perform primary or secondary re-completion operations.

Crimson VS Completion jobs can help reduce completion costs by up to 50% over conventional completion methods that depend on isolating packers and screens. These savings are accomplished by reducing rig time for initial completions. Subsequently, re-completion costs are also dramatically lowered by eliminating the need for a rig to perform a zone change in a well with multiple stacked pays. This combination of qualities makes the service particularly well suited for use in limited reserve intervals, small fault blocks, as well as in stacked pays. The new vent screen technology is also especially applicable in advanced initial completion design, re-completions for existing wellbore geometries, and remedial sand control on currently producing zones.

Conduct of operations

To drill the three wells, 31/2-in. production casing/tubing was run and cemented with the Surface Controlled Subsea Safety Valve (SCSSV) in place. After the rig was released, a 200-class jackup rig was mobilized with electric line and coiled tubing to prepare the wellbores for the completions. A cast iron bridge plug was correlated on depth with electric line to provide a base for the vent screen assembly. Each well was perforated, and the vent screen assemblies were put in place. Coiled tubing was used to place one of the assemblies across the interval, and wireline was used to place the other two.
Tree savers were fitted on each well and all wells were manifolded together. A treating line was run to the edge of the platform for the stimulation vessel. A total of 165,000 lbs of high density proppant with a surface modification agent (SMA) to limit proppant flowback was pumped sequentially into the three wells in less than 15 hours.

After the vessel was released, the proppant remaining in the monobore above the vent screen assembly was allowed to settle and cover the vent screen assembly. Following that, coiled tubing was run downhole to wash out the excess proppant to the top of the assembly. Once the coiled tubing was pulled out of the hole, the wells were turned over to production.

Exceptional results

Used in the West Cameron field to access bypassed reserves, the system generated substantial economic value, proving conclusively that higher-rate completions can be made with the vent-screen method without incurring sand production. The three wells in the West Cameron field are believed to be the first 31/2 in. monobores in the Gulf of Mexico, and had a combined initial rate of 42 MMcf/d of gas. At completion of the three-well project, the client had saved a significant amount of money and 105 days of operational time compared to conventional methods. Additional savings will be realized as the wells are re-completed to upper pay sands with rigless installation of additional vent screen completions.