Technical Information

Prodigy is currently using radial jet drilling technology in the completion of some of our the Austin Chalk wells, as opposed to horizontal drilling. This technology has been applied in other fields with excellent results (3 to 10 fold increase in production rates in comparison to those achieved from conventional vertical wells).

It is evident from the production histories and drilling and completion reports available for numerous wells drilled in the Austin Chalk that a poorly stimulated or unstimulated vertical completions can drain only a very limited area (generally less than 7 acres). However, drilling horizontally with a dip orientation has the potential to connect multiple vertical fracture systems within a single wellbore, resulting in drainage of a larger area and higher initial production rates.

In general, the development and application of horizontal drilling has proven to be highly successful in carbonate reservoirs, and in recent years, become the standard operating procedure used throughout the Austin Chalk Trend. Despite its obvious success, it is noted that horizontal drilling is a relatively expensive operation and involves a significantly higher degree of mechanical risk in comparison to drilling a vertical hole. Furthermore, a horizontal well is only able to target a very limited vertical interval when performed in relatively thick reservoirs such as the Austin Chalk. Consequently, a significant thickness of reservoir section, particularly the lower portion is potentially never in contact with the wellbore.

A relatively new completion technique known as radial jet drilling is able to overcome some of the shortcomings of horizontal drilling in carbonate and shale reservoirs. Radial jet drilling has seen limited application in the completion of the Austin Chalk in several nearby fields with excellent results (3 to 10 fold increase in production rates in comparison to those achieved from conventional vertical wells). Initially, a vertical hole is drilled through the zone or zones of interest, and the wellbore is subsequently logged and production casing set. Four lateral holes, approximately 1" to 2" in diameter and 300’ in length are then radially jet drilled at different levels within the prospective reservoir intervals. An exit hole is milled in the production casing and a lateral hole is cut into the target formation with a very high-pressure water jet.

The process first involves making up a deflector shoe, and running tubing in the hole to the desired depth with the deflector shoe attached. Next, the milling assembly is run in the hole and a 1 1/2" hole is milled in the casing. Afterwards, the jetting assembly, which includes a coil tubing unit and a jetting nozzle attached to a high-pressure flexible hose is installed and run into the well and through the deflector shoe so that it is positioned to pass through the hole milled in the casing. Once the jetting nozzle enters the pilot hole which was started with the milling assembly, water is pumped through the nozzle under very high pressure to jet the hole ahead of the nozzle. In addition to jetting forward, the nozzle is designed to direct a large portion of the jetting fluid at approximately 45 degrees from horizontal in a reverse direction.

The forward jets cut the reservoir rock and the reversing jets pull the nozzle and flexible hose into the reservoir. The jetting nozzle advances through most rock types at roughly 50’ per minute. After reaching a total depth of 300’ from the well bore, the jetting nozzle is pulled slowly back to increase the size of the jetted hole and clean any formation fines from the lateral. Once retrieved from the lateral and pulled from the hole, the tubing and attached deflector shoe can be turned from surface and the process repeated at a different azimuth at the same level in the wellbore. Once the desired coverage is achieved for any one zone (maximum of 4 laterals with 5 3/8" casing), the tubing and deflector shoe can be pulled up to a new horizon and the process repeated at the new depth. The process requires less than 100 gallons of water per lateral, so water invasion per foot of lateral cut is minimal.

Operational results achieved with equipment utilized by several different contractors show that 90% of attempted laterals reach the desired jetted length of 300’. Various subsurface conditions like the occurrence of large fractures, faulting, or highly deviated formations could be the cause of early termination of some laterals. In most cases, the tubing can be turned slightly, another hole milled, and a successful lateral jetted out 300’ at the same level. In almost every case where the equipment has been deployed, the target well’s productivity index with respect to all fluids has increased 3 to 10 fold in comparison to those achieved in a vertical well. The increase is attributed to the exposure of reservoir rock in as many directions as have been jetted.

Reservoirs having adequate permeability to allow uniform reservoir pressure distribution across the well’s drainage area usually experience lower productivity increases. Reservoirs, such as the Austin Chalk, that have lower permeability, and exhibit increasing reservoir pressure with increasing distance from the wellbore usually experience much larger production increases. Reservoirs having a large degree of secondary porosity (natural fractures or vugs) have a wide range of responses; but, in general, the more radial holes drilled, the greater the chance of connecting with these fractures or vugs and the greater the chance of having a successful result.

The lithology of the reservoir in which the tools were placed did not have significant impact on successfully jetting the laterals. Consistently, laterals were successfully jetted out 300’ in limestone, sandstone, and dolomite reservoirs. The few shale and coal seam reservoirs, where the technology was utilized, also had consistent successful results. In addition to the reservoir types, the relative geologic ages of the reservoirs did not seem to have an effect on success rate.

Radial jet drilling technology has been employed in several instances in conjunction with other stimulation techniques. Acid jobs and hydraulic fracture treatments have been executed after jetting laterals. Most of the wells that were completed with radial jet drilling and subsequently stimulated with acid or hydraulic fracture treatments exhibited substantial production increases when compared to their offset wells that had been stimulated with acid or fracture treatments alone. Inhibited acid can be transported much farther into the formation after the application of radial jet drilling, and if desirable, multiple fractures can be initiated 300’ from the wellbore in several different planes.
In conclusion, the application of radial jet drilling technology in the completion and development of the Austin Chalk is likely to significantly increase the ultimate recoverable reserves and initial production rates achievable for these formations (3 to 10 fold increases).