Oligocene Reservoir Research Articles

A Correlation of Electric-Log-indicated Reservoir Temperature With Actual Reservoir Temperature -- Southwest Louisiana

The indicated subsurface formation temperature available from an electrical log or other open-hole formation-evaluation log survey is nearly always lower than the actual temperature. However, in exploratory drilling, the log-indicated temperature frequently reflects the best available subsurface temperature information. A reliable figure for formation temperature for an exploratory well may be needed for completion design or a gas reserve estimate. The following is a discussion of a preliminary correlation developed for estimating preliminary correlation developed for estimating reservoir temperature from log-indicated temperature for wells in the 10,000 to 15,000-ft depth range onshore southwest Louisiana. The statistical correlation is shown as Fig. 1. It is a plot of reservoir temperature measured during the open-hole electrical log survey vs reservoir temperature measured during a cased-hole, shut-in bottom-hole-pressure survey for 36 wells. The 36 wells are gas wells belonging to 17 different operators. The wells are in Miocene, Oligocene, and Eocene age reservoirs in 20 different fields located in 10 parishes. All of the wells appear to have been logged under essentially similar conditions. In most cases, there was more than one log run, including a run at two or more different total depths. A maximum recording thermometer was used for both the cased-hole and openhole temperature measurement. In reviewing the log temperatures, it was noted that in most cases for a particular well, the same bottom-hole temperature was recorded for different log runs to the same depth on the same date. This indicates that a bottom-hole temperature was measured during only one of the log runs and thus precludes the estimation of actual subsurface temperatures from log temperatures using a previously suggested procedure. The use of a maximum recording thermometer on each log run is the responsibility of the operator as well as the logging company if the operator wants the information. Fig. 1 contains a line representing a least-square fit of the data points. With only one exception, the higher temperature was recorded during the bottom-hole-pressure survey. Based on the curve constructed and an arithmetic average of the data points, the log-measured temperature would have to be increased by 11.1 percent to equal the pressure-survey-recorded temperature. The pressure-survey-related temperature points for 26 of the wells were compared with the temperature as determined from available coverage provided by a published geothermal gradient map. This comparison is included as Fig. 2. It was made to aid in evaluating the cased-hole temperature points reflected in Fig. 1. For the most part, the temperatures in Fig. 2 show relatively good agreement. Ten of the temperature points in Fig. 1 were not used in Fig. 2 because points in Fig. 1 were not used in Fig. 2 because the geothermal contours did not extend into the parishes pertinent to that data. parishes pertinent to that data. Although this investigation is preliminary in nature, it indicates the following. Fig. 1 - Electric-log-indicated bottom-hole temperature vs shut-in bottom-hole-pressure survey indicated bottom-hole temperature, 10,000 to 15,350-ft depth range, onshore southwest Louisiana. (Data from 36 gas wells in 10 parishes.) Fig. 2 - Gradient-map-indicated bottom-hole temperature vs shut-in bottom-hole-pressure survey indicated bottom-hole temperature, 10,000 to 15.350-ft depth range, onshore southwest Louisiana. (Data from 26 gas wells in eight parishes.) P. 181

Significance of Pliocene Stratigraphic Paleontology, Gulf Coast: ABSTRACT

Major oil reserves of South Louisiana are found in Oligocene, Miocene, and Pliocene sandstone reservoir rocks. Increasing rate of sediment concentration in depocenters explains the hydrocarbon richness of the upper Miocene and Pliocene strata. This same factor led to increasing provincialism of faunas in post-Oligocene time. The paleontologists' problems in younger Tertiary strata are compounded by an apparent slowing of foraminiferal evolution. Whereas there are 20 regional Oligocene marker zones that divide about 10,000 ft of section, there are no more than five or six Pliocene zones to divide twice as thick a section. Recognition of temporal clines is vital to the stratigrapher who would subdivide an interval so nearly devoid of index species. Stratigraphic subdivision is not an end in itself, but is an indispensable step in the delineation of depocenters and depositional trends. End_of_Article - Last_Page 2039------------

Relation of Oil Occurrences at Surani, Rumania, to Origin and Migration of Oil: GEOLOGICAL NOTES

The preservation of oil residues in the depleted Oligocene reservoir sands of the Surani anticline is cited to illustrate the concept that a permanent (visual) record is left once oil has been present in a bed. Absence of such records in source rocks or in beds through which migration occurred might be due to expulsion of the oil from the source bed and migration in a state intermediate between the original organic material and the final product.