THE EDM FORMATION FLUID SAMPLING AND HYDRAULIC TESTING TOOLA REPORT ON ITS OPERATION AND DEPLOYMENT AT THE R-20 MONITORING WELL SITE
LOS ALAMOS NATIONAL LABORATORY
LOS ALAMOS, NEW MEXICO
Dr. William M. Turner
EDM SYSTEMS (USA)
September 20, 2002
Updated June 28, 2003
In ground-water-quality studies, the three dimensional distribution of analytes is required. This information is obtained most directly by drilling boreholes and collecting samples of ground water from the saturated zone. Fluid samples from saturated zones are collected by constructing monitoring wells, casing the monitoring wells, setting the casing with cement, shooting the casing with a wireline tool, installing a straddle packer over the selected zones, installing a pump and pumping water (if any) until conductivity and pH stabilize and then collecting the sample.
In drilling with a mud-rotary or foam system it is completely unknown whether and where perched water zones exist. Finding these zones may require completing a monitoring well and testing each zone.
The existing methodology is fraught with high cost, drilling problems, and uncertainty. Even when a test well is completed, it is unknown whether water-bearing zones were by-passed. Additionally, when the test wells are completed and abandoned, casing is left in the ground.
In the delineation of plumes of contaminated ground water, it is desirable to simply drill and pull water samples on the fly without pulling the drill pipe and conducting multiple other operations which add significantly to time and cost.
In ground-water exploration programs, water quality commonly varies with depth. That is, shallow poor quality ground-water may overlie deeper water of better quality. The lateral and vertical distribution of the interface between good and poor quality water may vary from location to location, and therefore be hard to predict. Even multiple boreholes within an area may fail to enable the identification of the interface. It is desirable to identify the interface at the well site. This is not easily or inexpensively done.
THE EDM TOOL AND ITS OPERATION
The EDM Formation Sampling and Hydraulic Testing (FAST) tool was developed to solve the problem of delineation of water quality zones at well sites in order to provide good quality water supplies in rural villages. The FAST tool can also be adapted to perform aquifer-performance tests or drill-stem tests at selected depths.
The FAST tool is constructed from stainless steel. It comprises a system of flaps and internal valves. The flaps and valves are actuated by pressure differences between the drilling fluid inside the drill pipe and in the annular space between the drill pipe and the boreface. While drilling small jets of drilling fluid continually flush and clean the sampling ports. On extraction of the FAST tool, these same jets of drilling fluid help break up the surrounding sand pack.
The FAST tool is used at the level from which a fluid sample is desired. For shallow sampling depths up to 1,000 feet, the sand pack is emplaced around and above the FAST tool by shoveling 10-20 sand into the annular space and allowing it to settle around the tool and above the drill bit. Below 1,000 feet depth, the sand is pumped through drill string. The amount of sand must be carefully monitored based on the volume of each pump stroke.
When the sand pack is emplaced around tool, pumping takes place from within the drill pipe. As the fluid level in the drill pipe lowers, the differential pressure thus created opens the ports in the FAST tool such that formation fluid can move through the emplaced sand pack and be pumped to the surface. A submersible pump inserted into the drill rod or an air lift system may be used depending on the drill string diameter and the depth to water. The sand pack isolates the fluid in the annular space from entering the sand pack and mixing with the formation water. The fluid level within the annular space will be unaffected by air-lifting or pumping from within the drill pipe if a properly designed drilling fluid is used. Fluid-level measurements in the annular space are necessary, therefore.
Figure 1 is a photograph of the FAST tool under test at our manufacturing facility in Germany.
Two German drillers experienced in the handling and operation of the FAST tool were brought in to supervise the use of the tool two weeks prior to the scheduled date of use about August 23, 2002. It was anticipated that they would train the drilling crew with a test well somewhere on the Navajo Reservation or in the Phoenix area. This did not happen.
The installation and the operation of the FAST tool was straightforward at the R-20 monitoring well site. The FAST tool was added to the drill string directly above the bit. Despite two weeks of planning the deployment of the FAST tool, the proper adapters to chase the 4 1/2-inch API regular box threads on the FAST tool were not available at the site. They had to be to be located and were rented from an oil field service company in Farmington, New Mexico. This caused a delay.
The FAST tool was deployed at 784 feet and drilling was begun in basalt using foam. This was the first time the tool had been used in rugged drilling of fractured basalt and it maintained its integrity. It was the first time the tool had been used with foam. The German drillers feared that the jets would become clogged.
The Puye Formation drilled without difficulty to 913 feet with the FAST tool. Drilling terminated because of problems with the drilling rig air compressor. This necessitated pulling the drill tools back into the casing at 780 feet. By the time the compressor was repaired and the hole re-entered some collapse of the hole in the Puye had taken place. To ensure a smooth bore hole for emplacement of the filter-pack sand in the annular space around the FAST tool, another 20 feet to 933 feet was drilled.
With the bit at 933 feet, we switched from foam to drilling fluid. However, the FAST tool required a high viscosity water-based drilling fluid.
Drilling mud was introduced and circulated to the surface. As soon as mud circulation was established 10, 50 pound sands of 10-20 mesh sand was shoveled into the annular space. This required moving some of the surface equipment at the hole to gain access to the annular space. About two hours were allowed for the sand to settle around the FAST tool.
It is necessary to know the fluid level in the annular space. Water-level-measuring equipment was available; however, probes have been lost in the annular space in the past and a protective tubing in the annular space was not available to measure the fluid level in the annular space. Knowledge of the fluid level in the annular space is critical to determine whether the sand pack is functioning. If the fluid level in the annular space drops as the fluid level in the drill string is lowered by pumping from within the drill string the sand pack is leaking from above. Consequently, when pumping from inside the drill string began, there was no way to tell if the sand pack had been isolated by overlying drilling mud.
A 3/4-inch airline was introduced into the drill string through a specially constructed head. The head allowed air-lifted water to exit into the mud pit along a return-flow channel dug into the soil.
The fluid level in the drill string was about 230 feet when air-lifting began. The airline was gradually lowered to a depth of about 350 feet in stages as fluid was blown from the hole. The production rate was established at about one gallon per minute at about 2100 hours on September 2, 2002. The discharge was stabilized to the satisfaction of Josef Grotendorst who has used the FAST tool elsewhere for 10 years. The test was carried out blind because fluid levels behind the casing could not be measured.
By 0020 hours on September 3, 2002, discharge terminated and the on-site crew lowered the 3/4-inch tubing to about 380 feet to re-establish discharge. Discharge terminated with the air line at 380 feet as well. Because discharge had terminated parties responsible for the project decided to terminate the test because of time constraints and costs.
To disengage the FAST tool and return to drilling, the drill string was raised about three inches and rotated about one-quarter to one-half turn in either direction. The mud pump was then kicked in at full pressure. The drill string dislodged and began to rise evenly. Return flow at the surface from the annular space occurred within several seconds indicating that the fluid level in the annular space between the casing string and the drill string had remained near the surface and that the sand pack had isolated the drilling mud in the annular space from the FAST tool and its open ports.. Within five minutes sand returns were observed in the return flow. Any sand not flushed from the borehole would have settled back into the rat hole formed when the first 40-foot section of drill pipe and the FAST tool were pulled.
The major problems were unfamiliarity of the drill crew and supervisory personnel with site setup and the drilling fluid requirements. Another problem was the tension among all parties (except EDM personnel) that the drill string would be sand-packed in the hole and that the hole would be lost. The concept of sand-packing tools in place is contrary to every belief of drillers throughout most of the world. When the FAST tool came free so easily, a collective sigh of relief and wonderment passed over the site.
Mechanically, the tool performed perfectly. When it was disassembled at the drill site it was internally clean and the internal valves were free and functional.
The reason for the failure to obtain a sample is not completely clear. The regional potentiometric surface was at 873 feet, based on later water-level measurements. The final pumping level in the drill string was probably about 380 feet.
Grotendorst insists that elsewhere ground water can be extracted from any depth even if the fluid pumping level in the drill string is above the regional potentiometric surface. He points out that this is due to the Law of Communicating Pipes and that the reason there was no water production or very little production was because the top of the Puye has so little water or extremely low transmissivity.
Both Dr. William Turner of EDM Systems (USA), Professor Bruce Thompson of the University of New Mexico and David Stewart of Stewart Brother Drilling Company in subsequent meetings were unable disagreed with the Law of Communicating Pipes and believe in keeping with Bernoulli's Equation that the air lift should have been below the expected depth of the regional water table. This is a minor issue, however.
Everything about the FAST tool is so counter-intuitive from the use of drilling mud to the sand-packing of drilling equipment in the hole to the effectiveness of the drilling mud to seal the top of the sand pack, to the valving within the FAST tool. It is clear, however, that an earlier version of the FAST tool has been successful elsewhere.
It was agreed by all that, based on conventional science and Bernoulli's Equation, if the airline had been below the expected regional potentiometric surface, water may have been produced if the upper Puye had favorable transmissivity.
Based on the conduct of the demonstration project, EDM has developed the following suggested protocols for utilizing the FAST tool for functional efficiency.
The FAST tool should be hydraulically tested to ensure that all flaps and valves operate and the pressures at which they actuate should be recorded. This activity can take place in the shop of the drilling company or a service company responsible for servicing and renting the equipment.
SITE PREPARATION - MUD PIT
In building the drill site a separate lined pit for the drilling fluid must be constructed.
INSERT FAST ABOVE DRILL BIT
The FAST tool is inserted on top of the drill bit that has an API regular pin thread looking upward. The drill pipe has API box threads looking downward. For ease of placement of the FAST tool it will be normally equipped with API regular box threads on the bottom end and API regular pin thread at the top end. If the FAST tool has a different configuration, appropriate crossover adapters must be on site prior to the initiation of drilling to assure no lost time in chasing threads or thread size.
RUN TOOLS TO BOTTOM AND BEGIN DRILLING TEN FEET ABOVE TOP OF TARGET ZONE
During drilling operations, if the FAST tool is in the drill string and drilling is progressing, drilling can be stopped at the interval to be tested and the sand-pack emplaced and the test conducted.. The borehole must have and even gage. If drilling has terminated for some period and sloughing of the hole is a possibility, the hole should be advanced another 10 feet.
PROVIDE ACCESS TO THE ANNULAR SPACE FOR PURPOSE OF FLUID LEVEL MEASUREMENTS
It is imperative to know in advance of pumping operations whether the fluid level in the annular space is stable following introduction of the sand pack material.
SET TOOL ON BOTTOM AND ADD 10-20 SAND TO SET SAND PACK AROUND TOOL AND ABOVE FIRST DRILL COLLAR. ALLOW ONE HOUR PER 400 FEET FOR SAND TO SETTLE
It is necessary that the drill bit be on the bottom of the hole to form the sand pack around the FAST tool and the drill pipe or drill collars. Sand is added to the annular space and allowed to settle through the drilling fluid.
INSTALL PUMP INSIDE DRILL STRING AS NEAR TO FAST TOOL AS POSSIBLE AND BELOW DEPTH OF SUSPECTED POTENTIOMETRIC SURFACE
The FAST tool is actuated by pressure differences between the inside and outside of the tool. The pump should be set, in our opinion, at least below the expected regional potentiometric surface. If the depth to the potentiometric surface is unknown, the pump or air line should be set as close to the top of the FAST tool as possible. If no fluid is recovered we should be able to say that the rock unit does not contain recoverable water.
USE ELECTROSUBMERSIBLE WHERE POSSIBLE
The FAST tool has been extensively used elsewhere. Under normal conditions, drill pipe having 4.5-inch inside diameter is used. A 4-inch diameter electrosubmersible pump is used to extract the drilling fluid and formation water from inside the drill pipe. The electrosubmersible pump is able to sustain higher production rates than air-lift pumping.
AIRLIFT PUMPING AND USE OF POLYETHYLENE PIPE
Genuine air lift pumping requires an air pipe and an eductor pipe. Air is jetted upward inside of the eductor pipe. For maximum effectiveness, the length of the airline pipe inside of the eductor pipe must be calculated.
The modified air lift used by most drillers simply involves the use of the drill string to blow air into the hole. This method places an air pressure against the boreface and can restrict entrance of air into the annular space between the drill pipe and the boreface. Surging the air can offset this.
If it is sought to use the drill pipe as the production string with the introduction of air through an airline, water above the mouth of the airline is simply lifted. Depending on pressure and air-flow rate, a bubble may develop beneath the end of the airline in the drill string. Water can channel past the air bubble and will be blown to the surface.
Care must be exercised in using polyethylene airline. Friction loss of air flow in the pipe must be considered. That is, air-flow rates must be low enough to ensure that the pressure at the entrance to the air line does not exceed the burst strength of the air line particularly bearing in mind that the friction loss will heat the polyethylene pipe and reduce its burst strength.
When air lifting begins, there is no hydrostatic pressure difference between the interior and exterior of the polyethylene pipe. As the fluid level inside the drill string drops, the pressure difference between the inside and outside of the air line increases. Care must be taken to ensure that the pressure difference does not exceed the burst strength. This latter problem will be more important at and near the surface. The pressure profile of the air line will begin at a maximum at the compressor and drop to the hydrostatic pressure difference at the mouth of the air line. For example, a 3/4-inch polyethylene pipe with an inlet pressure of 125 psi can only move about 20 cfm to the mouth of the pipe although the air compressor is rated at 50 cfm. If the air line is 800 feet long, it can only move about 14 cfm.
8/31/02 17:15 Assemble the FAST tool and run tool to bottom.
8/31/02 2120 FAST tool on bottom at 784 feet
9/01/02 0045 Begin drilling out basalt 784 to 824 feet using foam using 8 3/4-inch tricone button bit.
9/01/02 1710 Drilled to 913 feet in the Puye with foam and switched to drilling mud.
9/02/02 1120 Drill 20 feet into Puye to 933 DM tool.
9/02/02 1745 Adding sand to sand pack the FAST tool (5-inch OD) and at least one 6-inch drill collar above the tool. gpm.
9/02/02 2100 Discussion as to whether to try to collect Puye water sample. Agreement was obtained to run test until pumped water was clear or until 0600 on 9/03/02.
9/03/03 0022 No water production.
9/03/02 0515 Circulate drilling fluid to break FAST tool and drill string free from sand pack and circulate sand out of hole.
9/03/02 0610 Begin tripping out.
9/03/03 0920 All rods, collars, FAST tool out of hole.
UPDATE - AUGUST 25, 2003
On June 28. 2003, EDM filed for a U.S. Patent on improvements and innovations to the original patent that permit the FAST -OAG Tool to be used in oil and gas applications at depths of 15,000 to 20,000 feet to carry out multiple formation testing and sampling without being withdrawn from the hole. At the same time, EDM has filed PCT application for protection of its intellectual property in some 120 countries worldwide.
UPDATE - JANUARY 2, 2004
On December 16, 2003, EDM Systems (USA) was granted U.S. Patent 6,662,644 B1 on the FAST tool.
EDM Systems (USA) is in the process of licensing the technology.
Dr. William M. Turner