Commercial Application of Steamflooding in an Oilfield Comprising Multiples Thin Sand Reservoirs
Authors: Powers M.L. , Dodson C.J. , Ghassemi F. , Moore J.S. 
Published: December 2007

Steamfloods conducted in thin reservoirs generally provide marginal profits because of relatively high field provide marginal profits because of relatively high field development costs per barrel of oil in place (OIP) and excessive heat losses from the productive zone. New techniques are being used to solve these problems, such as use of induced horizontal fractures to circumvent the detriments attributable to thin zones and to solve the problems of steam distribution and confinement inherent problems of steam distribution and confinement inherent in any steamflood.

This paper documents the successful application of steamflooding in the multiple thin-sand reservoirs of the Loco Unit, Stephens County, OK. These reservoirs occur at depths from 50 to 1,200 ft [15 to 366 m] and range in thickness to 40 ft [12 m]. Porosities of the productive zones vary from 20 to more than 30%, and permeabilities range from 100 to more than 4,000 md. Oil gravities of the various zones range from 16 to 24API [0.96 to 0.91 g/cm3]. Table 1 presents average reservoir properties of the three most important zones in the area of principal interest. Reservoirs that occur at depths above approximately 700 ft [213 m] have little or no natural reservoir energy and generally contain viscous oils, ranging up to 10,000 cp [10 Pa.s]. Consequently, there was no primary production from these reservoirs, and potential for waterflooding was marginal. Steamflooding has been the only recovery process applied successfully to these zones, except for one isolated instance. Reservoirs at depths greater than 700 ft [213 m] normally contain lower-viscosity oils. Six of these zones were produced by solution gas drive and were later waterflooded successfully. After 23 years of water-flooding, two of these six zones have been tested and have proved to support commercial steamflooding operations.

Introduction

The Loco field is situated on a northwest-southeast trending anticline that underlies a major portion of Township T3S-R5W, Stephens County, OK, at approximately the location indicated in Fig. 1. The field was discovered in 1913, and sporadic development occurred from that time until the 2,300-acre [931-ha] unit was formed in 1961 for the pursuit of secondary recovery operations. From 1961 through 1964, the field was developed on 10-acre [4.05-ha] spacing, and water-flooding of the six deepest zones was initiated, using 20-acre [8.09-ha], five-spot patterns.

Geology and Reservoir Description. Twenty-four identified zones have been proved to have, or are suspected of having, significant oil saturation in at least some areas of the unit. The most significant of these are illustrated in the log section of Well 511 presented in Fig. 2. The various oil sands have been named alphabetically ascending (As, Bs, Cs, etc.) and descending (Ad, Bd, Cd, etc.) from the Loco lime (LL), which occurs at a depth of 800 to 900 ft [244 to 274 m]. Three zones (X, Y, and Z) of minor areal extent are located between the LL and the A-shallow (As) sand.

The LL and the five deep sands are of Hoxbar-Pennsylvanian age. A fault trending northeast-southwest displaced this interval approximately 100 ft [30 m]. The original OIP in the six deep zones is estimated to be 73.4 × 10(6) bbl [11.7 × 10(6) m3]. These zones have had primary recoveries of approximately 3 % of the original OIP, and waterflooding, which was initiated in 1961, will ultimately recover an additional 11 %.

The shallow sands, which lie above the LL, are of Pontotoc-Permian age and are not affected by the Pontotoc-Permian age and are not affected by the faulting. Minimal natural reservoir energy has precluded significant primary recovery, and the adverse mobility ratios inherent to the native oil viscosities make waterflooding generally impractical. A notable exception to this rule was a 20-acre [8.09-ha] waterflood of the As and Cs zones, which was conducted in the southeast quarter of Sec. 9 from 1956 to 1963; this was a marginally profitable operation. No response was observed in a profitable operation. No response was observed in a 10-acre [4.05-ha] X-zone waterflood, which was operated during this time interval in the southwest quarter of Sec. 9. From 1969 through 1972, pilot waterfloods were conducted in the As, Bs, Ds, and Js sands, none of which were successful.

JPT

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