Sub-optimal wellbore cleanup can cost millions

Once a well is drilled, cased, and cemented, the hard part is over, right?

Ghiselin
GhiselinDick Ghiselin • Houston

Once a well is drilled, cased, and cemented, the hard part is over, right? Wrong. Perhaps this was the case several decades ago, but there has been a sea change in well construction. Today's deepwater, high-pressure/high-temperature (HP/HT) completions often represent the most costly and most risky part of the job. Completions are not necessarily more risky from a safety standpoint, but can be extremely risky from a cost and impaired productivity standpoint.

What seems to be a relatively straightforward task can turn into an operator's worst nightmare if done improperly. This was the theme of the recent M-I SWACO launch of its SMART 3D displacement service. The service is intended to offer a single source comprehensive transition from drilling fluid to completion brine that overlooks nothing that could impair installation of the completion or subsequent production from the well. It is a 3D service that integrates chemical, mechanical, and hydraulic techniques with a thorough design enabled by the company's Virtual Completion Solutions (VCS) modeling software.

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Complete cleanup saves time and money

Recently, a North Sea operator experienced unexpected costs in a critical offshore open-hole completion. Poor debris management during the displacement phase made it impossible to access the formation isolation valve (FIV). This forced an unplanned wireline intervention involving a tractor-deployed bailer to clean out debris clogging the valve.

Utilizing the SMART 3D displacement service on subsequent wells in the field, the operator was able to save 20 days and several million dollars worth of non-productive time. In addition, wells cleared of debris prior to completion came online within three days compared to the 12 days previously required, and fluid costs were reduced by 30%.

By modeling the displacement job in advance, completion engineers are able to come up with the exact combination of chemicals in the form of debris pads, cleaning solvents, and surfactants to prevent cross-contamination of drilling fluid and costly completion brines to make trouble-free transition from drilling to completion fluids. Multi-purpose one-drum displacement fluid that is compatible with both oil- and synthetic-base drilling fluids cleans the pipe and leaves it water-wet. Completion specialists are able to deploy the best combination of mechanical scrapers, brushes, and filters to dislodge and capture tough debris. Powerful magnets pick up all ferrous residue and bring it to the surface for disposal. Lastly the hydraulics of the pumping schedule are tuned to accomplish the transition in a single, smooth displacement.

Specialty tools run in conjunction with the displacement string to perform dressing of liner tops and polished bore receptacles leaving a smooth, clean surface for setting the packer. A unique tool allows inflow and negative testing of the liner top on a single trip performed in conjunction with displacement.

An impressive arsenal comprised of 10 combinable tools from the SMART 3D suite help engineers put together the optimal work string to complete all cleaning and displacement operations in the most cost-effective way for the particular well and situation under consideration.

It is not necessary to use all the tools all the time. The software helps engineers choose from the array of combinable tools to achieve their objectives in the most cost-effective way.

Production boosted six-fold

In one California field, the standard completion procedure involved drilling the pay zone using oil-base mud; then running a completion liner and displacing the cement with lease water. The well was completed by perforating and stimulating the formation with acid; then setting the production packer. Before stinging into the packer, the lease water was displaced with nitrogen, tubing was landed, and the well was put on production. The technique was characterized by incomplete cement removal and residue from the oil-base mud. These factors combined to severely restrict production.

Completion engineers designed a one-trip cleanup and displacement technique using SMART 3D solutions. Mechanical cleanup tools took care of the cement residue and solid waste accumulated in the rathole. A chemical spacer swept out oil-base mud residue and left the tubulars water-wet. To optimize hydraulics, the pumping schedule and chemical spacers were modeled beforehand using VCS software to achieve optimum size and chemistry for most effective cleaning, and filtration equipment strained solids from the lease brine. Three wells were cleaned up, placed on production, and each exceeded expectations. Overall production improved by a factor of six.

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