In horizontal wells completed as open holes that are irregularly shaped or badly washed-out, or with slotted or pre-perforated liners, mechanical packers can not be used to isolate a water- or gas-producing zone. Consequently, a new method using chemical packers has been developed and tested. The method involves:setting two chemical wellbore plugs in the horizontal section to straddle the problem zone,squeezing gel into the problem zone, andcleaning out the borehole prior to production.
Using coiled tubing, the whole operation would be conducted in one roundtrip.
The new method was tested using a 60 ft. long horizontal-well apparatus consisting of an outer 12–3/4 in. PVC casing containing two concentric metal screens (ID's 9 in. and 6 in.). Space between the screens was packed with sand, forming a 6-inch wellbore with a 1–1/2 inch thick formation, into which a 4–1/2 inch pre-perforated liner was placed. A gel-placement tool was placed inside the liner. The tool consisted of a 1–1/2 inch tubing to spot/squeeze the formation gel, an internal ¾ inch tubing to spot the wellbore plug, and outer rubber elements for focussed gel placement. Model temperature was set at 110°F by circulating hot water through the apparatus.
Two runs were made, each consisting of spotting a 40 ft. long K-MAX wellbore plug, followed by spotting and squeezing PERMSEAL across 20 ft. of the borehole. (From symmetry, the placements represent a dual wellbore plug each 40 ft. long straddling a 40 ft. problem zone). After the formation gel had set, the apparatus was disassembled, showing the chemical plug had completely filled the borehole, strongly adhering to the borehole surface with no slumping. The formation gel penetrated and consolidated the formation. The tests confirmed the viability of the new zone isolation method that is planned for field-testing.
Introduction
The two main types of horizontal well completions are open-hole and slotted- (or preperforated-) liner completions. An open-hole completion is the most basic and simplest completion method. Open-hole completions may be utilized in strong and consolidated formation where borehole collapse or sloughing is not expected to occur. In weak or poorly consolidated formation, where borehole collapse and sand production problems are expected, a horizontal well would be completed with a slotted- or preperforated-liner. For some formation, borehole collapse or sand production problems may occur in later time as a result of production or reservoir pressure depletion. Slotted- or preperforated-liner completions may be gravel-packed to alleviate sand production problems.
Open-hole and slotted or preperforated liner completions suffer from one main disadvantage in that the producing intervals along the horizontal section are in direct communication with one another. One or more of the producing intervals may begin to produce extraneous gas (for an oil well) and/or water. For a horizontal oil well, the extraneous fluid production may be caused by one or a combination of the following:the horizontal section has been inadvertently drilled too near the oil-water contact or gas-oil contact,water and/or gas coning, andwater and/or gas production from a high-permeability interval (e.g. a fracture).
