Production From Horizontal Wells After 5 Years
Authors: Reiss L.H. 
Published: December 2007

The first of four horizontal wells drilled by Elf Aquitaine during the last 6 years produced its first barrel of oil in Aug. 1980. The others followed between 1981 and 1983. There is now enough production history to draw conclusions, some of which are surprising.

Introduction

Horizontal drilling is not a new concept; considerable effort was directed toward horizontal drilling during the 1950's and 1960's, mostly in the USSR. At that time, however, the results in terms of well production were rather disappointing. The current focus on horizontal drilling, which began in the late 1970's, resulted from the combined effects of improvements in directional-drilling techniques and the need for new oil. The originality of this approach is its adaptation of horizontal wells to definite reservoir engineering targets. Its uniqueness is that it leads, at least for Elf Aquitaine (in association with either the Inst. Francais du Petrole or the AGIP) to prolific oil wells.

Information gained during the drilling of horizontal wells in Europe between 1979 and 1983 pertaining to drilling, coring, logging devices, and reservoir engineering has been presented in other papers. However, very little has been published about the production behavior of these wells. Their production histories are production behavior of these wells. Their production histories are now long enough (2 to 5 years) to allow analysis. Reiss et al. noted that "of the four horizontal wells, the first two, Lacq 90 and 91, were devoted to mastering drilling, completion, and measurement techniques. Production was, of course, hoped for, but as a secondary result. The fourth well, Castera Lou 110, had been designed to master deep drilling problems, as well as completion; good production was hoped for. The third well, Rospo Mare 6D, drilled production was hoped for. The third well, Rospo Mare 6D, drilled by the Elf Italian subsidiary and AGIP, was strictly aimed at production purposes." production purposes."This horizontal production study is the main topic of this paper.

Production Behavior of the Wells Production Behavior of the Wells This section presents field reservoir engineering information and the production records of the horizontal wells; all are pumped and not selectively completed.

Lacq Superieur Oil Field.

The Lacq Superieur oil field is located in southwestern France. The reservoir lies at a depth of 610 m [2,000 ft]. The initial oil column amounted to 100 m [330 ft]. In the area where the horizontal wells were spudded, rock porosity and permeability are about 20% and 1 md, respectively. Oil viscosity is permeability are about 20% and 1 md, respectively. Oil viscosity is 17 mPa.s [17 cp].

This field has produced oil with an increasing water cut for 25 years. It is swept; its average water cut now amounts to 98 %.

Areally, the reservoir is made up of two distinct but communicating formations; i.e., a highly fractured dolomite--productivity index, J = 1 m3/(kPa.d) [50 bbl/(psi-D)]--and almost nonfractured limestone lenses--J = 0.01 m3/(kpa.d) [0.5 bbl/(psi-D)].

Lacq 90 Horizontal Well. The production history of Well Lacq 90, as well as the average of its vertical neighbors (including the dry wells located within the external boundary of the southwest lens), is shown in Fig. 1. The daily oil production of Lacq 90 is about three times greater than that of its typical vertical neighbor. This is consistent with the theoretical calculations made with Eq. 1.

A strong interference has been noticed between Lacq 90 and the best producer of its area, Lacq 44, which suggests the existence of a permeable channel between them. Lacq 90 might produce predominantly from this permeable section. predominantly from this permeable section. Lacq 91. Lacq 91 (Fig. 2) has successively crossed chalk ("head"), dolomite, and chalk again ("tail"). The chalk was expected, but the highly fractured dolomite was not. The productivity indices of these sections are about 0.01, 2.3, and 0.01 productivity indices of these sections are about 0.01, 2.3, and 0.01 m3/(kpa.d) [0.5, 100, and 0.5 bbl/(psi-D)], respectively. Selective completion of this well was partially successful because the head had been satisfactorily cemented and the fractured dolomite plugged (it had appeared to be filled by water). This allowed the plugged (it had appeared to be filled by water). This allowed the tail to be produced for some time; the lowest water cut of the field was 90%. Then the cementation of the head, as well as the plugging of the fracture, was destroyed accidentally by further acid plugging of the fracture, was destroyed accidentally by further acid treatment.

The well is currently producing mainly from the fractured dolomite; its productivity index, J, is about 2.3 m3/(kPa.d) [100 bbl/(psi-D)], with a 99% water cut. This high productivity has allowed production of Lacq 91 through a centrifugal pump at very high production rates and low pressures. The daily oil production amounts to 15.8 m3/d [100 B/D], which is the total oil production of this northeast lens of the field. But the low pressure does production of this northeast lens of the field. But the low pressure does not allow production of the less-productive head and tail, which need high production drawdowns to display industrial rates.

Castera Lou.

The Castera Lou oil field is located in southwestern France (see Fig. 3). The reservoir where the horizontal well, Well Lou 110, was spudded is a poorly fractured or nonfractured dolomite, the Breche de Garlin. It lies 2896 m [9,500 ft] below sea level and has a 70-m [230-ft] -thick oil column overlying a water-bearing formation. It has been produced for 4 years through three vertical wells.

Rock porosity and permeability are about 10% and 0.5 md, respectively. Oil viscosity is 1.5 mPa.s [1.5 cp]. The horizontal well has crossed the reservoir over 335 m [1,100 ft]; then complete mud losses, indicating the presence of open fractures, occurred. They were subsequently plugged.

The production records (Fig. 3) show that the daily oil production of the horizontal well is about five times greater than that of its typical vertical neighbor. This is consistent with the calculations made with Eq. 1.

Despite a very high production drawdown (6 MPa [60 atm]), Well Castera Lou 110 produced oil almost 1 year before the water breakthrough. At that time, the cumulative oil production was close to 10 000 m3 [63,000 bbl]. We believe that a horizontal tight lens protects the well against the vertical motion of the water crest (or protects the well against the vertical motion of the water crest (or horizontal cone).

We also believe that Castera Lou 110 currently produces from the nonfractured portion of the reservoir. We intend to continue producing until this area is completely flooded; then we will try producing until this area is completely flooded; then we will try to unplug the fractures and to produce some oil from them.

JPT

P. 1411