Lopatin's Method To Petroleum Exploration 2

The American Association of Pelroleum Geologists Bulletin V. 64, No. 6 (June 1980) P. 916-926, 13 Figs.. 4 Tables

Time and Temperature in Petroieum Formation: Application of Lopatin's iMethod to Petroieum Exploration^
DOUGLAS W. WAPLES^ AlMtract N. V. Lopatin in the Soviet Union has developed a method for taking t)oth time and temperature into account as factors in thermal maturation ofkerogen. Lopatin's time-temperature index of maturity (TTI) values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons. Because such information Is potentially of great Interest for oil exploration, a calibration and evaluation have tjeen made of Lopatin's method. Within the limitations of the data presently available the following statements can be made: 1.The rate of the chemical reactions involved in thermal maturation of organic material appears to double with every I C C (18°F) rise In temperature. 2. Threshold values of Lopatin's time-temperature index of maturity (TTI) are: 15 75 160 ~500 ~ 1,000 ~ 1,500 >65,000 Onset of oil generation Peak oil generation End oil generation 40° oil preservation deadline 50° oil preservation deadline Wet gaspreservation deadline Dry gas preservation deadline

conditions under which hydrocarbons could be generated and preserved. CONSTRUCTION OF GEOLOGIC MODEL Implementation of Lopatin's method begins with a reconstruction of the depositional and tectonic history of the geologic section of interest. This is best accomplished by plotting depth of burial versus geologic age, as shown in the hypotheticalexample in Figure 1. It should be remembered that such reconstructions are not geologic cross-sections. In the example in Figure 1 a Lower Cretaceous sediment was deposited 125 m.y. B.P. at the sedimentary surface (depth = 0). Since its deposition the sediment has had the time-depth history shown by the sohd line in Figure 1, moving from left to right. Its history consisted of continual depositionat varying rates until 80 m.y.B.P., at which time a brief (2 m.y.) uplift occurred in which the sediment was raised from a depth of 7,000 ft (2,134 m) to 6,000 ft (1,829 m). UpUft was followed by renewed subsidence until a depositional hiatus was reached at 20 m.y.B.P. The hiatus persisted until 6 m.y.B.P., when subsidence commenced again. The sediment is at present (time = 0 m.y.B.P.) at a depthof 10,500 ft (3,200 m). The line in Figure 1 thus

3. TTI values calculated from Lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemlsts. Potential applications of Lopatin's method for oil exploration include timing of oil generation, calculation of volume of hydrocarbons generated within a basin, and determination of economicdeadlines.

BSTRODUCnON It has been generally established in recent years that both time and temperature are important factors in the process of oil generation and in the subsequent cracking of oil to methane. In 1971, N. V. Lopatin in the Soviet Union published a paper which described a simple method by which the effects of both time and temperature could be considered in calculating the thermalmaturity of organic material in sediments. He developed a "time-temperature index" of maturity (TTI) to quantify lus method. Lopatin's original work was greeted with some enthusiasm and much criticism. Some of the problems which surfaced could be attributed to the poor quality of the data with which Lopatin originally calibrated his model (Neruchev and Parparova, 1972; Golitsyn, 1973; Karpov et al,1975). Despite these technical details, Lopatin's basic idea has merit. It was therefore decided to attempt to coordinate Lopatin's method with other parameters which relate to oil generation to devise a model which could predict the thermal

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