LOCATING AND CONTROLLING WATER PRODUCTION IN HORIZONTAL

. Basic horizontal

well design in McElroy was a re-entry of an existing vertical wellbore and drilling medium radius

lateral(s) with 4 ¾” open hole completions

. Designs included 600 to 1000ft laterals drilled at 2 to 5

degrees from true horizontal to expose multiple layers of an overall 30 to 40 ft thick target zone.

(Figure 1) A major challenge was to understand the true impact of horizontal producing wells in

this waterflood setting which required some degree of evaluation to determine a fluid entry profile

over the length of lateral and build sections. Neither practical nor effective logging procedures

were available for wells requiring artificial lift methods, thus mechanical isolation and short term

swab testing was utilized to understand fluid entry and to explain well performance. Inflatable

packers are an integral component in the evaluation design due to the nature of the open hole

conditions. Large 200 to 600 ft long sections of the laterals were isolated independently using a

bottom inflatable bridge plug and an upper inflatable production packer. Swab testing or short

term full drawdown production testing provided a basic indication of fluid entry rates and oil cut.

After moving inflatable equipment and testing various portions of the open-hole wellbore, a

completion design using inflatable isolation assemblies were used to exclude zones of excessive

water entry and optimize oil production. Basic test objectives have remained the same over the

past 4 years, however the equipment and methods have evolved to reduce costs and improve

accuracy and efficiency.

Continued development of inflatable tools and production testing methods resulted in recent tests

using a new approach to improve fluid entry testing process. Re-settable inflatable straddle

packers combined with a hydraulic jet pump provide full drawdown testing on short intervals. This

new method allows for testing multiple zones under full artificial lift drawdown with a single trip in

the hole. Initial field trials demonstrated a major advance toward improved efficiency and

reduced cost of evaluating well fluid entry.

EARLY EVALUATION METHODS

Initial production testing of newly drilled horizontal wells with the full length of the curve and

lateral exposed frequently showed surprisingly poor results. Swab testing before the initial

completion regularly showed 100% water production. Swabbing rates were not sufficient to draw

the fluid levels down in the well due to high formation productivity. Initial tests using electric

submersible pumps as the artificial lift method showed low oil cuts, high fluid levels and water

rates 2- 5 times that of surrounding vertical producers. Wells that showed some or complete loss

of circulation while drilling (fresh water drilling fluids with reservoir pressure of 600 – 800 psi)

were typically the worst performing wells during initial testing. Drilling data and initial testing

observations clearly indicated problems with undesirable water entry along the lateral portion of

the well. A mechanical isolation and swab test procedure was designed to determine if the

zone(s) of excessive water entry could be located. Inflatable packers were used to provide

isolation, and swab testing was used to determine fluid entry rate and oil cut. A very coarse

evaluation with three intervals, the curve and two segments of the lateral was the typical design

that met testing objectives at acceptable levels of cost. The zones at which lost circulation

occurred during drilling sometimes dictated how the lateral would be segmented for testing. Mud

log data, drill rates, lithology, and oil fluorescence data was also regularly used to pick packer

seats and assist in test zone determination.

Setting inflatable packers in this process proved to be relatively simple and reliable in the open

hole. Inflatable packers used as bridge plug were configured with bull plugs and on/off tools to

allow for disconnecting and retrieval. Retrieval has been 100% successful. Inflatable production

packers were re-settable to allow for expanding or reducing the test interval if necessary. Once

packers were installed, swab testing was expected to be ideal for obtaining simple and effective

results. Although swabbing proved to be a low cost approach, it was found inaccurate and

misleading. In wells with low reservoir pressure and/or high inflow condition, swabbing was not

effective in creating sufficient drawdown to achieve inflow from tighter oil bearing zones. Oil cut

results were often pessimistic with only traces or no oil shows present. At best, swabbing proved

to be a good indicator of the water entry zones when the fluid level could not be pulled down. The

potentially productive intervals were readily recognized because they could be swabbed down to

various degrees and often showed 5 – 20% oil cut during swabbing. This method of evaluating

fluid entry was slow, expensive, and was not successful in achieving accurate and definitive

results. It did however, prove to be a highly valuable step in a successful well project. The

qualitative findings were able to show oil production that was not present during initial well testing.

It was able to provide important information resulting in improved decisions on the productive

potential of a well, and the feasibility of further investment.

Typical testing by this method took up to 1-2 days per test interval and frequently required 10 to

12 days of rig time to complete a cursory evaluation the well.

A MODIFIED APPROACH TO FLUID ENTRY EVALUATION

Because of shortfalls in swab testing method, the testing procedures were modified in two basic

ways. First, individual zones were tested for extended periods using ESP pumping equipment to

achieve full drawdown. Secondly, test tool configurations were designed with straddle packers,

seating nipples and sliding sleeves so that fewer packer sets were needed to accomplish the

testing plan. The use of submersible pumps with variable speed drive units provided good

flexibility to test zones with different inflow performance at full drawdown conditions. The duration

of ESP tests were lengthened to ensure valid, stabilized oil cut results. Although test results

improved significantly, frequent pulling and re-running ESP pumping equipment was time

consuming and expensive. (Figure 2) summarizes a case history for this type evaluation.

Re-settable, inflatable, straddle packer systems were also introduced into the testing efforts and

provided a process to test multiple zones without pulling out of the hole to redress tools and

packers. (Figure 3) A packer spacing of 200 ft was used. Swab testing each isolated interval

was again attempted as the necessary way to determine fluid entry and oil cut. Straddle packers

worked quite well in improving the efficiency of isolating different zones and allowing for a more

complete wellbore evaluation. Although the desired results of efficient multiple tests was

achieved, swab testing again proved inaccurate and generally prolonged testing efforts. This

evaluation method showed excellent potential in wells where swab testing would be effective.

Depending on the length of the lateral and the desired test information required, spacing could be

lengthened or shortened. A typical test could result in 10 to 25 zone tests with good wellbore

conditions. These modifications in testing methods and tools began to solve many of the

problems encountered, but there still had to be a better process to meet all the objectives.

The inflatable packers overall, performed well in achieving competent hydraulic seals in the open

hole. The Grayburg reservoir is a dolomite formation with good compressive strength. Some

difficult hole conditions were encountered (i.e. oval hole, key seats, and washouts), however most

wellbores were found to be competent, gauge and suitable for trouble free testing. Packer setting

was generally reliable with few function problems and element failures were rare. Use of different

setting mechanisms as well as new element technology improved tool reliability. Because packer

seats cannot be pressure tested on open hole situations, a practice of picking up and slacking off

10,000 lbs was adopted to help verify solid packer seats. Fluid movement through the nearwellbore

area, around the 4-foot packer elements has not been recognized as a problem.

MECHANICAL WATER SHUT-OFF COMPLETION OPTIONS

Once water entry and oil productive intervals were delineated, three basic completion designs

were used to control water entry. The type of mechanical control device depends on where the

water is found in the lateral. Water found at the toe can be controlled by an inflatable bridge

plug/cement retainer. (Figure 4) Water production found in the lateral can be controlled by a scab

liner. (Figure 5) Water production found in the toe and heel of the well can be controlled by an

inflatable bridge plug/cement retainer at the toe and a scab liner in the heel. (Figure 6)

TESTING OF THE JET PUMP STRADDLE PACKER METHOD

A reliable, re-settable test tool including an artificial lift method was required to determine a

producing profile and make water shutoff decisions. The simplicity and reliability of a hydraulic jet

pump were coupled with inflatable re-settable straddle packers. The ultimate intended use of this

tool was to test open hole horizontal wells, but the initial well selected was a vertical cased hole

well with multiple perforations.

The tool string was configured with three packers and a jet pump. (Figure 7) The bottom two

packers isolated the test interval and the top packer isolated perforations from the produced and

power fluid returns producing up the casing annulus. The jet pump is placed in the string just

above the top packer. A remote setting head above the jet pump and inflatable packers is

connected by a ¼” stainless steel inflation line, insuring that all three packers function

simultaneously.

Once the tool string is made up, it is lowered to the desired set depth. The jet pump is pumped

from the surface to the carrier and is seated. Continued pumping results in increased tubing

pressure and is held at approximately 800 psi to inflate the packers. Simply slacking off on the

work string traps inflation pressure in the elements. Continued tubing weight is applied during this

test.

Power fluid rate and pressure to the jet pump are adjusted to establish drawdown and production.

Power fluid along with produced fluid return to surface via the tubing-casing annulus. Both power

fluid and produced fluid rates are measured with the difference equaling production rate. If no

extra fluid is produced, then that zone is deemed nonproductive and the tools are moved. If the

hole is full, casing volume is calculated to determine when actual bottoms up fluid can be

expected at the surface. For the McElroy tests, produced fluid was calculated to reach the surface

in 1.5 hours. Bottoms up fluid is not necessary on all tests to determine fluid entry and production

rates, but is necessary if oil cuts are to be determined. If the produced rates are low, the

perforations can be grouped in later tests to obtain good oil cut data. If the hole is empty, bottoms

up fluid will be the first produced.

After testing each zone, moving tools to the next test interval required less than 30 minutes. The

only difficulty encountered while restarting a test, was a loss of blanket gas in the test separator.

Care should be taken to assure that all valves on the surface equipment are closed when moving

tools.

The initial intent was to test the tool configuration and workability in a vertical well before running

in a horizontal well. After experiencing the effective and reliable tool function, seeing the quality of

the test results and the ease of obtaining them, this method of testing was deemed very

applicable to testing vertical cased hole wells.

Acidizing during the test procedure can be done without pulling the tools. The jet pump is

removed and replaced with a blanking sleeve, test zone stimulated, sleeve pulled and jet pump

replaced. Spent acid is then produced and the zone re-tested.

JET PUMP DETAILS

Jet pump offers several advantages as the artificial lift means. A wide range of test rates can be

achieved with one pump size. The pump size can be easily changed to match the well production

and a broad range of jet pump sizes is available. The pump can be easily removed from well by

reversing it out of the hole or pulling it with the sand line. Inefficiency in power fluid use is not a

problem during short duration tests versus running the pump for a permanent artificial lift

application. Power fluid can be oil, field water, produced water or any readily available,

compatible fluid.

SURFACE EQUIPMENT

•

Portable test separator for fluid handling.

•

A propane tank to supply blanket gas pressure for instruments and fluid dumping on wells

producing low gas volumes.

•

A pump and filter with output of 1.5 bpm at 3000 psi. In this example, the available workover

rig pump was used.

•

Storage tanks for power fluid, produced water and produced oil.