Abstract

This paper describes a process that has improved production, reduced costs, saved time, and dramatically improved the results of fracture stimulating low permeability horizontal wells. The use of both propped and acid fracture treatments will be described.

The process has been used for openhole completions aligned in the approximate direction of fracture propagation as well as for fractures transverse to the well bore. The technique has effectively eliminated well bore connectivity problems that had been observed in vertical completions and cased and cemented horizontal wells with transverse fractures.

The process has been used to increase production over 25 fold in a 30 year old field. It has also proven successful in a marginally economic field that had been completed using propped fractures in vertical wells.

The procedure employs a system of multiple, retrievable treating subs that are specifically tailored to a unique well bore configuration and allow treating the entire interval with a single stage. The treating subs are designed to distribute the treating fluid as desired along the length of the lateral. The process has been successfully used in over 100 wells and laterals in fields located in California, Illinois, New Mexico, Utah, and Texas.

Introduction

History of Horizontal Wells^1,2.

Horizontal and high angle wells have been envisioned and/or used for approximately 80 years. Patents were filed in the early 1920's in the United States, but the tools were never fully developed. Horizontal wells re-emerged in the 1940's and 50's, but were displaced when hydraulic fracturing was developed in the late 1940's and early 50's. Horizontal wells were used in the Soviet Union and China during the 1950's and 60's. A heightened interest in horizontal well resurfaced in the late 1970's due to the increased directional control developed for offshore drilling. By 1985 further advances in horizontal drilling techniques and production response led to a boom in horizontal wells.

Well Paths¹.

Many different well paths are considered “horizontal” besides a flat path. Common trajectories include inclined, both up and down, wavy or undulating, multilevel, and multilateral, or depending on the application very complicated. Fig. 1 shows some of the more common well paths.

Common Uses^1,2,3.

Horizontal wells increase production by contacting more reservoir rock; intersecting natural fractures; reducing gas or water coning at a given production rate or drawdown; improving sweep efficiency in secondary and tertiary recovery projects; and improving gravity drainage in low pressure reservoirs. Ideally, the horizontal well should be completed openhole to take full advantage of the increased reservoir contact. This is not always possible due to wellbore stability problems or undesired fluid entry.

Unstimulated Wells^1,3.

Horizontal wells are cost effective where the reservoir permeability is sufficient, damage is not excessive, or sufficient natural fractures are encountered to produce economically. Completions are relatively simple when these key parameters are encountered and stimulation, isolation of undesired gas/water, or wellbore stability is not a problem. However, when these problems exist, the complexity of the horizontal completion increases dramatically. Isolation requires that additional hardware such as external casing packers, scab liners, screens, slotted liners, etc. be used in an effort to eliminate the unwanted reservoir problem.

History of Horizontal Wells^1,2.

Horizontal and high angle wells have been envisioned and/or used for approximately 80 years. Patents were filed in the early 1920's in the United States, but the tools were never fully developed. Horizontal wells re-emerged in the 1940's and 50's, but were displaced when hydraulic fracturing was developed in the late 1940's and early 50's. Horizontal wells were used in the Soviet Union and China during the 1950's and 60's. A heightened interest in horizontal well resurfaced in the late 1970's due to the increased directional control developed for offshore drilling. By 1985 further advances in horizontal drilling techniques and production response led to a boom in horizontal wells.

Well Paths¹.

Many different well paths are considered “horizontal” besides a flat path. Common trajectories include inclined, both up and down, wavy or undulating, multilevel, and multilateral, or depending on the application very complicated. Fig. 1 shows some of the more common well paths.

Common Uses^1,2,3.

Horizontal wells increase production by contacting more reservoir rock; intersecting natural fractures; reducing gas or water coning at a given production rate or drawdown; improving sweep efficiency in secondary and tertiary recovery projects; and improving gravity drainage in low pressure reservoirs. Ideally, the horizontal well should be completed openhole to take full advantage of the increased reservoir contact. This is not always possible due to wellbore stability problems or undesired fluid entry.

Unstimulated Wells^1,3.

Horizontal wells are cost effective where the reservoir permeability is sufficient, damage is not excessive, or sufficient natural fractures are encountered to produce economically. Completions are relatively simple when these key parameters are encountered and stimulation, isolation of undesired gas/water, or wellbore stability is not a problem. However, when these problems exist, the complexity of the horizontal completion increases dramatically. Isolation requires that additional hardware such as external casing packers, scab liners, screens, slotted liners, etc. be used in an effort to eliminate the unwanted reservoir problem.