AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain
The Main Results of Investigation of the Crystalline Basement of the Tatarstan
(1) Geological Faculty, Department of Geology of Oil and Gas, Kazan State University, Kazan, Russian Federation.
The reservoirs of the basement have been studied, although the technology of studying the Precambrian is yet to be improved.
Now, Tatarstan boasts of numerous wells drilled down to the crystalline basement, which indicate that petroleum exploration at great depths does make sense. All previous evaluation of the crystalline basement’s prospects have been primarily based on the conventionally conducted drill-stem formation tests (DSFT). However, oil and gas inflows from the crystalline basement of the Dnepr-Donetsk trough showed that the sole use of DSFT results for evaluating the hydrocarbon potentials can be erroneous. Moreover, the available drilling data from deep wells show that excessively high repressuring and the use of loaded drilling mud can drive filtrate deeply into the reservoir. When the drilling rate is low, the time interval between penetration and testing of prospective zones becomes quite long. If reservoir pressure is equal to or is lower than hydrostatic, mud solution penetrates the reservoir and forms seals, preventing formation fluid from flowing out during DSFT procedures.
Efficiency of hydrocarbon exploration within the Precambrian crystalline basement can be substantially increased through the use of 1) a special drilling technology to minimize penetration of drilling mud into the decompacted/fractured zones of the basement, 2) solutions that would minimize the influence of drilling fluid on capacity and filtration properties of the reservoir, and 3) specific methods of inflow stimulation and reservoir studies of the strata with various lithologic, petrographic and reservoir properties.
Seismic profiling and deep sounding revealed that the crystalline basement has a lamellar-and-scaly structure. Main reflecting horizons have been found to occur below impermeable rocks at a depth of 5 to 7 km. Hydrocarbon fluids can be channeled into oil fields through the basement’s fractures and faults. Hydrocarbon relics from the fractured/brecciated zones indicate that the fluids could have been driven from the lower horizons to the upper ones by the temperature field and the processes of compression and decompression.
An obvious depth-related growth in amount of gas, a widening spectrum of methane’s homologs, greater amounts of methane’s heavy ones, such as pentane and hexane, and the appearance of helium.