Turtle Bayou 1936-1983: Case History of a Major Gas Field in South Louisiana
Authors: Cronquist Chapman 
Published: December 2007

Cronquist, Chapman, SPE, Cronquist Assocs.

Turtle Bayou field, located in the middle Miocene trend in south Louisiana, is nearing the end of a productive life spanning more than 30 years. Discovered by Shell OilCo. in 1949 after unsuccessful attempts by two other companies, the field is a typical, low-relief, moderately faulted U.S. Gulf Coast structure, probably associated with deep salt movement. The productive interval includes 22separate gas-bearing sands in a regressive sequence of sands and shales from approximately 6,500 to 12,000 ft[1980 to 3660 m]. Now estimated to have contained about1.2 trillion scf [34 × 10 std M ] of gas in place, cumulative production through 1982 was 702 billion scf[20 × 1O std M ] . Cumulative condensate/gas ratio(CGR) has been 20 bbl/MMcf [11O X1O M /M . Recovery mechanisms in individual reservoirs include strong bottom water drive, partial edgewater drive, and pressure depletion. Recovery efficiencies in major pressure depletion. Recovery efficiencies in major reservoirs range from 40 to 83% of original gas in place(OGIP). On decline since 1973, it is anticipated the field will he essentially depleted in the next 5 years.

Introduction

This paper is a review of the geological development and reservoir performance of a major, multi reservoir gas field with a variety of producing mechanisms, Geological development is reviewed by reference to three papers published between 1955 and 1964. Reservoir performance is reviewed by comparing actual performance with that anticipated in my 1963 study, performance with that anticipated in my 1963 study, prepared while employed by the operator. prepared while employed by the operator. It now appears that actual gas recovery will be about6 % more than estimated in 1963, at which time about 15 %OGIP had been produced. The 1963 estimates are compared with 1983 "actual" in Tables 1 and 2. Field total and totals for six of the major reservoirs in the field are included. To my knowledge, a detailed case history of this type of field has not been published. This material may be useful to those with interests in gas accumulations incomparable geologic settings.

Geological Development

Turtle Bayou field is part of the Turtle Bayou/KentBayou/North Turtle Bayou complex, which is located in south Louisiana, about 65 miles [105 km] southwest of New Orleans (Fig. 1). Geophysical prospecting in the area in the 1930's apparently indicated a structural anomaly. In 1936, Humble Oil and Refining Co. drilled Continental Land and Fur (CLF) No. 1 in the southeast corner of Sec. 25, T-17-S, R-13-E (Fig. 2). The well reached a totalledpth of 10,254 ft [3125 m] and was plugged and abandoned. Five years later, Stanolind Oil and Gas Co. drilled CLF No. 1 about 4 miles [6 km] to the southeast, in Sec.34, T-17-S, R-14-E. This well was plugged and abandoned at a total depth (TD) of 11,010 ft [3356 m]. Asobserved by Brown, "These two points of control showed a rather flat condition existing between the two wells which might have been interpreted as gentle nosing."In 1942, Humble drilled CLF No. B-1 about 2,000 ft[610 m] southeast of their first test. This well was dry and abandoned at 11,343 ft [3457 m] TD. This well encountered the objective section considerably deeper than the two previous tests. Noted Brown, ". . . [this] could best be explained by north dip from the Stanolind well and ‘down-to-the-coast’ faulting between [the two Humble wells] . . . the fault could not be detected from the electric logs of either well." Humble's last test in the area was drilled northwest of their original location. This well added little to the structural interpretation and was plugged and abandoned at 11,268 ft [3435 ml TD. plugged and abandoned at 11,268 ft [3435 ml TD. The discovery well for the Turtle Bayou field was drilled by Shell Oil Co. in 1949, CLF No. 1 was drilledin Sec. 32, T-17-S, R-14-E, to 11,432 ft [3484 m] TD, penetrating several of the major productive sands. The penetrating several of the major productive sands. The well was completed through perforations in a side trackedhole (12,002 ft [3658 m] TD) from 11,980 to 11,988 ft[3652 to 3653 m] in what later was designated "BB "sand. On initial potential, the well flowed 2,750 Mscf/D[78 × 1O std M /d] through a 1/4-in. [0.6-cm] choke[flowing tubing pressure (FTP)] 3,550 psi [24 MPa], CGR23 bbl/MMscf [130× 10 M /M] 48 degrees API [0.8g/cm 3 ]. The structural interpretation shown in Fig. 2reflects subsurface control available in 1949. Previous operators had drilled deep enough, but off the crest of the structure, thereby missing a productive area of about3,000 acres [1215 ha]. By 1955, Shell had drilled seven more producers and a dry hole in Turtle Bayou field, and Union Producing Co. had discovered Kent Bayou field, immediately to the west (Fig. 3). The structural interpretation reflects a north-south, rather than an cast-west, fault between the two earlier Humble wells. In addition, observed Brown,"Although there is no available cut out in any of the wells drilled to date, there is strong evidence that this structure is bordered on the north by a large 'down-to-the-coast'fault."

JPT

p. 1941