HORIZONTAL WELL BUOYS OKLAHOMA UNIT OIL FLOW

A horizontal well drilled in an Oklahoma unit in which gas reinjection is in progress has increased the unit's oil production more than four fold.

The No. 71 well in West Cement Medrano Unit near Cyril has been producing at a rate of about 1,800 b/d of oil since being placed on production Apr. 23, said Phillips Petroleum Co., operator of the unit.

The well boosts unit production to about 2,000 b/d, compared with 454 b/d before startup of the horizontal well. It is producing 37 gravity oil from Pennsylvanian Medrano sandstone at 6,048 it true vertical depth.

The well can produce at much higher rates, but Phillips is maintaining 1,800 b/d because neither gas nor water coning are evident at that rate. Phillips believes the current production rate could be maintained for as long as 5 years without significant coning.

The well, in giant Cement field of Caddo County, is believed to have the highest production rate of any current well in Oklahoma. Overall success of horizontal drilling could prolong unit life 20-30 years from the present, Phillips said.

Phillips has picked locations for as many as four more horizontal wells in other fault blocks in the 3,700 acre unit and could propose one to the 140 or so working interest owners later this year.

HORIZONTAL PROJECT

The 71 well bore lies 170 ft below the present gas-oil contact and 80 ft above the present oil-water contact, said Jim Johnson of Houston, Phillips' reservoir engineering director for Oklahoma and Central Texas.

The Medrano reservoir has a gas cap drive and a low pressure of 350 psi, permeability averaging 200 md, and dip of 23. All produced gas has been reinjected since the 1940s.

The 71 well's horizontal section is 4,068 ft long, excluding the radius. Completion was made through 7 in. slotted liner with seven external casing packers. No treatment was necessary.

All signs are positive to date, and drawdown appears to be very low, Johnson said.

Nine vertical wells that had been producing a combined 241 b/d of oil lie along the horizontal well bore in the unit's Block B. Those wells were shut in and likely will be used later as observation wells.

During the next few weeks Phillips plans to run production logs to confirm that the entire length of horizontal well bore is producing, switch to a permanent pump, and monitor fine details of production performance.

The project shows that Phillips is "still very interested in mature oil and gas producing areas in this country and can develop unique ways for increasing domestic oil production and reserves in a manner that competes economically with imported oil," said John Whitmire, Phillips senior vice-president for exploration and production.

DRILLING PROGRAM

The 71 well is the first drilled since the 1960s in the unit, which has produced more than 41 million bbl of oil since field discovery in 1936.

Phillips ran surveys to pinpoint bottomhole locations of the nine vertical wells, then drilled the horizontal well between rows of four and five wells, avoiding the vertical bores of wells that had been fractured years earlier.

Phillips spudded the 71 well early in February, kicked off and built angle at 70/100 ft. At 53 it drilled an 80 ft tangent for the submersible pump, then built angle at 10/100 ft. It cemented 9-5/8 in. casing at 68 in the curved section.

Time from spud date to drill the well, run slotted liner, and displace the hole with completion fluid was 73 days, said David Beardmore, drilling engineering specialist.

Phillips used water base mud in the vertical section and oil base in the curved and horizontal sections. With the low formation pressure, oil base mud reduced the risk of stuck pipe or formation fracturing. Torque and drag were minimal.

Formation dip made steering difficult in the 12-1/4 in. hole, and steering was much easier in the 8-1/2 in. hole, Beardmore said.

Main unit working interests are held by Phillips 27-31%, Pennzoil Co. 18.72%, American Exploration Co. 18.5%, Cheyenne Petroleum Co. 9.48%, Amerada Hess Corp. 9.03%, Fina Oil & Chemical Co. 5.51%, and Maynard Oil Co. 5.01%.