簡介：應用液體射流技術的原理非常簡單：通過增加水平和豎直方向上井筒與油藏的接觸面積，提高原油開采速度，增加原油采收率。

The theory behind applied fluid jetting is simple: to increase production rates and improve reservoir recovery rates by maximizing the reservoir area contacted by the well bore, both vertically and horizontally.

Blast AFJ Rig positioned over the well and preparing to begin lateral jetting process. (Images courtesy of Blast Energy Services Inc.)

A key issue facing most independent oil and gas producers is how to economically increase their production volumes. Conventional approaches can involve some fairly expensive undertakings such as in-field drilling programs, horizontal drilling, well stimulation, and massive frac jobs. While these programs may apply to large fields with thick contiguous pay sands, there are many fields with thinner sand sections or lower flow rates where the potential improvement may not support such high-dollar solutions.
Applied fluid jetting (AFJ)

Over the past several years, Houston-based Blast Energy Services Inc. has been developing a downhole stimulation service that “may have” the potential to dramatically increase production volumes from existing or newly drilled wells at a cost-effective price.

In recent months, with their prototype coiled tubing (CT) rig and specialized downhole equipment, they have successfully horizontally jetted up to 90 ft (27 m) into targeted oil or gas zones from the vertical well bore. In addition to receiving some technical assistance from Reliance Oil and Gas, the parties formed a revenue-sharing agreement to begin testing the stimulation service on wells operated by Reliance. This case study moves the theory closer to commercial realization. Blast has patents pending for the AFJ process.

During the initial test in October 2008 and at a well depth of approximately 300 ft (92 m), the rig completed two separate 50-ft (15-m) laterals in each of two gas wells located near Abilene, Texas. The horizontal laterals were positioned at 180º from each other into the targeted producing sand. As a result, the initial natural gas production increased five-fold on the first well and 12-fold on the second well.

Unfortunately for the operator, these wells came in as gas producers and were too far from a pipeline system to justify building a spur. Encouraged by both technical success and the resulting production volume improvements, the company moved the rig to the Austin Chalk play in South Texas near the town of Luling.

Austin Chalk Applications

The rig was contracted by the operator to laterally jet two newly drilled wells at approximately 2,750 ft (839 m) of vertical depth, where two productive zones were logged in the Austin Chalk. Drilling cuttings were laid out by depth and determined to have oil shows.

The proprietary deflection shoe was set on the end of the 27⁄8-in. production tubing string and hung at the deeper zone open hole at approximately 2,750 ft (839 m). The jetting technique involved running a pressurized cutting fluid through the CT string into the braided stainless steel flexible CT hose while circulating fluid between the CT and the production tubing to aspirate the cuttings generated from the AFJ process. The company has deliberately constrained the lateral reach of the flexible hose to 90 ft (27 m) to avoid the additional Texas permitting requirements when drilling horizontally longer than 100 ft (31 m), a requirement which is usually applied to conventional horizontal drilling.

Each area has its own distinctive lithology, and the cutting fluid is custom designed for the specific application. Unlike on the wells near Abilene where diesel fuel was primarily used as the jetting fluid due to the amount of clay in the producing formation, an acid based solution was used in the Austin Chalk formation. Lateral displacement was achieved by a combination of fluid pressure and acid dissolution of the limestone rock formation. The targeted zone thicknesses in the Austin Chalk wells were between 6 and 12 ft (1.8 and 3.7 m), so it was crucial that the path of the lateral remain in the narrow formations and stay relatively perpendicular to the vertical well bore.

Four laterals were jetted in the deepest zone at 90° angles from one another and lengths approaching 90 ft (27 m) were achieved. Each lateral took less than one hour to perform. The rate of penetration was deliberately slowed in the range of 1.5 ft (0.5 m) per minute to insure the lateral went straight ahead and stayed within the target zone.

In the next zone up-hole, three laterals were successfully jetted. Unfortunately a malfunction in one of the rig’s pumps damaged the flexible hose. The pump was repaired and jetting continued with a 50 ft (15 m) back-up reel of flexible hose. The jetting assembly was brought up-hole to the shallow zone, and another three laterals were successfully jetted.

The first well in the Austin Chalk achieved eleven laterals in the upper, middle, and lower zones. Similarly, 10 laterals were jetted on the second well in the Austin Chalk.

During the jetting process, oil was seen on the pits containing the circulated jetting fluids and the wells “kicked” after the laterals were drilled. In addition to the Blast Rig #1, auxiliary equipment employed included a large water tank, an acid truck, and a vacuum unit to circulate fluid into the mud pits while jetting.

The acid solution remained in the lateral formations for a few weeks before well fracturing operations commenced in order to facilitate micro-fracturing in the formation rock. The purpose of the frac is to drive sand into the lateral well bores to maximize the initial production flow rate and overall production longevity.

Results

Typical South Texas Austin Chalk wells vertically drilled to this depth have initial flow rates of only 5 to 10 b/d of oil. After fracturing operations were completed and over 7,600 barrels of frac fluid was produced, the oil produced in the wells began to increase daily. At the time of this article’s publication, each well was producing daily flow rates of 33 b/d of oil. Based upon the results thus far, the operator expects that over the next few weeks the daily production rate could more than double the typical rates from newly drilled wells in this area of South Texas. Such results will dramatically improve the operator’s economic performance of vertical wells in the Austin Chalk and allow operations to expand into new and existing fields in the area that were previously considered economically marginal. Furthermore, this expected doubling in production rates will become a great marketing tool to other operators with openhole completions in the Austin Chalk or other similar limestone formations.

Next steps

It is believed that applied fluid jetting can work successfully in many types of sandstone and limestone/carbonate formations. In addition, the process may have potential as far down as 8,000 to 9,000 ft (2,440 to 2,745 m) of vertical depth, although this has yet to be proven.

While currently focused on openhole completions, Blast Energy Services also plans to offer stimulation programs for targeted zones behind pipe. In this case, milling operations will first be conducted by a workover unit to open the formation up to AFJ operations.

Meanwhile, the company has already begun to capture additional drilling opportunities, including the execution of a recent agreement with Resource Energy Technologies in Kentucky where the AFJ process is expected to significantly increase natural gas flow rates from shallow limestone formations similar to the Austin Chalk.