HORIZONTAL DRILLING SCORES MORE SUCCESSES

Feb. 26, 1990
Guntis Moritis Drilling/Production Editor The Journal's second exclusive compilation of horizontal drilling projects under scores that this technology is receiving worldwide acceptance, and the number of wells drilled continues to accelerate rapidly. The following pages document many of the wells drilled in 1989 and the 1990 plans of operating companies.
Guntis Moritis
Drilling/Production Editor

The Journal's second exclusive compilation of horizontal drilling projects under scores that this technology is receiving worldwide acceptance, and the number of wells drilled continues to accelerate rapidly.

The following pages document many of the wells drilled in 1989 and the 1990 plans of operating companies.

As in OGJ's previous survey (OGJ, Feb. 27, 1989), this year's survey primarily includes wells drilled with horizontal laterals in the producing reservoirs that are longer than 1,000 ft. Both new wells and recompletions of existing wells are included.

The maximum angle of the horizontal laterals listed varies from 79.5 to 104.

MORE, DEEPER, LONGER

The 130 wells listed in this survey are only a part of all horizontal wells drilled. Wells with less than 1,000-ft horizontal laterals were in general excluded, and some small independents working in the Austin chalk trend in Texas did not respond to OGJ's survey.

The Texas Railroad Commission has, for example, identified 12 small operators (see box) in the Austin chalk who have tested horizontal wells; another 19, not listed, have permits to drill. However, because the primary intent of the survey is not simply to count wells drilled, but to reveal drilling practices, the lack of response is not too important in this case because the respondents do describe the typical practices in the chalk.

The drilling activity in the Pearsall (Austin chalk) field in South Texas has been described as "hysterical." Leasing costs have jumped from $20-50/acre to $200-500/ acre.

From virtually no rigs operating in the area, over 40 rigs, including large workover rigs, are at this writing drilling horizontal laterals in both new and old holes. One estimate is that 80 rigs may soon be working in this area.

RECORDS

A number of new drilling records were set in 1989. Unocal drilled the longest horizontal lateral to date. Offshore California, its Point Pedernales well A-16 has a horizontal section extending for 5,743 ft in the reservoir. Maximum angle is 87.5. This surpassed the previous record of 4,013 ft by Esso Resources Canada Ltd. in its Norman Wells K-50X well, drilled in 1987.

The 12,740-ft horizontal displacement of the Unocal well is the longest to date for a horizontal well. Also, as an extended-reach well the displacement is the longest drilled offshore California. Because the true vertical depth is a shallow 4,420 ft, about 10,000 ft of well bore was drilled at angles above 800.

The Unocal well is completed with a cement liner. This completion allows producing the furthest 1,000-ft portion of the hole first. And as water encroaches, that portion will be sealed and a new zone opened for production.

Unocal's Point Pedernales well is classed as a long-radius well. For a medium-radius buildup, the well with the record for the longest horizontal displacement is Oryx Energy Co.'s Stroman-Harris No. 2. Drilled in the Pearsall field, the horizontal displacement length is 4,164 ft, 4,110 ft horizontally within the reservoir.

With short-radius techniques, SELM (Montedison group) has drilled horizontal laterals over 1,000 ft. Its Vega 18 well, offshore Sicily, has a 6-in. horizontal lateral with a length of 1,053 ft. The length of the build curve was 216 ft, and the maximum build rate was 51.5/30 m (Fig. 1). Directional control was done with 4 1/2-in. measurement-while-drilling (MWD) tools. The horizontal section was logged with dual laterolog resistivity and microspherically focused tools conveyed on drill pipe.

Subsequently, Vega 5 (not listed in Table 4) drilled a 1,221-ft horizontal lateral. This is currently the world record length for a short-radius well.

The horizontal well that has the highest production rate is Norsk Hydro's 16T located in block 31-2 offshore Norway. The well was drilled to test the feasibility of producing a relatively thin (22 m) oil column under a large gas accumulation in the Troll field. The well is flowing 30,000 bo/d to the production test ship "Petrojarl." This production rate is roughly 10 times more than would be expected from a vertical well.

Norsk Hydro plans to produce the well for 1 year before deciding whether to develop the oil column with additional horizontal drilling. Harald Norvik, president of Norway's Statoil, largest oil producer in the North Sea, predicted during a recent trip to the U.S. that horizontal drilling will completely change the economics of North Sea oil development.

In another well in the North Sea, one of Shell Internationale Petroleum Maatschappij's operating companies, Nederlandse Aardolie Mij. B.V. (NAM), has drilled the deepest horizontal lateral. The FD-103 well on Block L-13, offshore The Netherlands, has a true vertical depth of 11,484 ft. The 83 horizontal lateral extended for 2,858 ft.

Last year's survey had Meridian Oil's 33-19H well in the Bicentennial field of North Dakota as the deepest at 10,796 ft.

PEARSALL FIELD

One of big successes in horizontal drilling has been the Pearsall field (Fig. 2) in South Texas. Oryx Energy Co. started the boom. In OGJ's tabulation (Table 4), information on 21 of Oryx's wells is summarized in one entry.

As of January, 12 of Oryx's wells had been completed, 4 were being tested, and 5 were being drilled. Oryx's plans for this area include drilling an additional 64 wells during 1990.

During the week ending Jan. 4, Oryx's production from 15 of its horizontal wells averaged 7,200 bo/d and 4.3 MMcfd of gas. By year-end, Oryx expects to be producing 15,000-20,000 bo/d from the Austin chalk.

Table 1, from Oryx's application to change the field rules, demonstrates the substantial increase in production that can be obtained from horizontal drilling.

The Pearsall field also provides a good case study for horizontal drilling potential in reservoirs that previously had been exploited. Since 1936, almost 2,000 wells have been drilled in the field, and the cumulative oil production is nearly 60 million bbl or just 30,000 bbl/well.

More than half of these wells were drilled because of advances in hydraulic fracturing technology in the mid-1970s, followed by the drilling boom resulting from oil prices jumping to $30/bbl during the early 1980s.

Now in the new boom, some wells with horizontal laterals have already exceeded cumulatives of 100,000 bbl, and some might have surpassed 300,000 bbl.

Oryx's well J.B. Baggett No. 13 with a 2,250-ft horizontal drainhole produced 112,400 between the completion date in April 1988 and Aug. 13, 1989.

The ultimate recovery is expected to be about 375,000 bbl.

The initial potentials of a number of wells are also impressive. Oryx's Heitz No. 1 tested 3,262 bo/d, and Winn Exploration Co.'s Leta Glasscock No. 10 flowed 5,472 bo/d. GLC Energy Inc.'s C.A. Beaver No. 1 in 24 hr tested over 3,000 bo/d, and during the initial 90-min test recorded rates of around 6,400 bo/d.

FIELD RULES CHANGE

The Texas Railroad Commission's temporary field rules for the Pearsall (Austin chalk) field will allow producing the horizontal wells at about 4.1 bo/d/acre. The acreage is determined in increments of 40 acres and calculated by the formula A = (L x 0.08126) + 80. A equals the calculated area assignable to a horizontal drainhole for proration purposes. L is the horizontal distance, in feet, between the point at which the drainhole penetrates the top of the Austin chalk and the horizontal drainhole end point within the Austin chalk.

As an example, wells with L of 1,477 - 1,968 ft are assigned a proration acreage of 240 acres. For an L of 2,953 - 3,444 ft, the assigned acres is 360. In these two cases the maximum daily oil allowable is 984 and 1,476 bo/d, respectively.

If multiple laterals are drilled, the temporary field rules allow the summation of the lengths if the angle between the laterals is greater than 90. The temporary field rules were effective on Aug. 22, 1989, and will remain in effect until Aug. 22, 1990.

DRILLING WHILE PRODUCING

One of the unique features of drilling in the Pearsall field is that hydrocarbons are commonly produced while extending the well laterally. Most of these wells are drilled with fresh water or brine to prevent formation damage. Because of either lost circulation into fractures that had previously produced, or encountering fractures with higher pressures, both oil and gas will enter the well bore during drilling operations.

Rigs are typically equipped to flow oil to storage and gas to a flare. Drilling while holding pressure on the annulus is common. To date, no major problems have occurred, although any time hydrocarbons are around the drill floor there is a reason to exercise utmost caution.

OTHER ACTIVITY

Another horizontal drilling boom is the fractured Bakken shale in North Dakota. Meridian Oil Co. is the most active operator in seeking to developed the 1 to 8--ft thick reservoir.

Production rates are not as spectacular as in the Pearsall field, but some wells are producing above 500 bo/d. As Meridian has gained experience in drilling horizontal wells, costs for these wells have decreased from 2.5 times to 1.2 times the cost of a vertical well.

During 1991-92, Elf Aquitaine has plans to add a third platform in the Rospo Mare field in the Adriatic that will be developed with 16 horizontal wells.

For 1990, Elf plans to drill about one horizontal well per month.

In January 1990, three horizontal wells (Oman, Angola, and Rospo Mare) were being drilled.

The six wells listed for Alberta Oil Sands Technology & Research Authority (Aostra) were drilled in a novel approach from underlying tunnels. The oil in the reservoir is highly viscous, 1 million cp at 50 F. Steam is used to stimulate the production. Although the producing rates are confidential, Aostra does indicate that the results from this small-scale pilot are excellent and that future plans for 1990 include drilling six more wells at the same site. The horizontal length of the new wells is planned to exceed 1,000 ft.

Saskatchewan is the only place that had wells (listed in Table 4) completed with multiple tubing strings. Both of Sceptre Resources Ltd.'s wells, and Mobil Oil Canada's well, had two strings of tubing.

Coring is not common. Only eight wells in our survey had cores taken; three were drilled by Maersk Olie OG Gas AS off Denmark, three by Shell, and one each by Husky Oil and Mobil. The Shell and Mobil wells were all in Saskatchewan.

Eleven wells in the survey were hydraulically fractured, some with acid. Four of these jobs were done by Maersk in its wells offshore Denmark. Another three were performed by Union Pacific Resources in the Giddings field, Texas. Eight wells were acidized.

1990 PLANS

Horizontally drilled wells are still a small percentage of the approximately 50,000 plus yearly worldwide completions (not including the U.S.S.R. and some Eastern European countries). But the number, as shown in Tables 2 and 3, is growing.

In Table 2 our survey shows that in 1990, 39 companies plan to drill 376-393 wells with horizontal lengths greater than 1,000 ft. Laterals shorter than 1,000 ft are definitely less attractive. From Table 3, only 14 companies have plans to drill 26-28 wells of this type.

As was mentioned earlier, the frantic drilling activity in the Austin chalk is difficult to tabulate at this time. Possibly several hundred more horizontal wells could be drilled there during 1990.

This Texas setting of an old time drilling boom is a fitting preamble to mushrooming activity that is becoming more international in scope.

Copyright 1990 Oil & Gas Journal. All Rights Reserved.