The Role of Fault Seal of Middle Miocene (Chokrak Formation) Fields at Northern Edge of West Kuban Trough in Fluid Migration Throughout Reservoir Development

Abstract

One of the basic objects of exploration works and hydrocarbon extraction in Krasnodar territory in recent decades are Chokrak depositions in the northern edge of West Kuban Trough. About twenty light oil and gas condensate deposits were discovered there. In the 90's and 2000's the major scope of seismic studies and drilling activities were concentrated in this direction. Most of the fields discovered are related to tectonic (disjunctive) faults and deformational traps. Genetically disjunctive tectonics is represented by listric faults having their roots in middle-upper Maikop and their flattening in Sarmatian-Meotic stratum. Faults have great influence both on deposit formation, and on the process of hydrocarbon extraction. It is necessary to understand and forecast fluid penetrating ability of disjunctive dislocations in order to create and improve geological models both during exploration works, and in the course of field development. The estimation of breakdown pressure value sufficient for tectonic disturbance fracturing can be also used during drilling of wells with a view of reducing risks of drilling mud loss and loss of circulation. Productive sandstone units of Chokrak formation of Temryuk syncline fold in West Kuban Trough are represented by terrigenous depositions of the subsea detrital fans (Fig. 1). They are characterized by lenticular structure. Thickness of sandstone units is between first several metres to the first several tens of meters (typically 4-8m), and for clay seals it is the first tens of meters. By their zones reservoirs are limited to slope (northern edge) and distal (axial part of West Kuban Trough) detrital (alluvial) fans (cones). The distinctive feature of Chokrak fields is their abnomarly high pore pressure and reservoir pressure (anomaly ratio is up to 2), intensive tectonic desturbances (Fig. 2) and various extent of filling for traps and reservoir units/sequences (often incomplete filling). Fluid saturation differences between sand units and neighboring tectonic blocks, as well as elastic (volumetric) drive, which is unlikely for development in tectonic sealed pools, result in situations, when it is necessary to improve the hydrodynamic model of fields that is to find out the sources of watering and formation energy. Inter-bed overflows across faults can represent one of such sources. If we define fluid permeability of tectonic disturbances it is possible to determine a source of formation energy and water, to make more precise calculation of reserves in the fields being developed and more reliable saturation forecasts for adjacent tectonic blocks, reducing thereby further exploration risks. That is why FSA (Fault-Seal Analysis) was applied. Fault Seal Analysis has appeared at the intersection of several oil and gas disciplines -geology, geophysics and reservoir engineering. 3D survey data and their interpretation results are used in this analysis as well as well logs, core structure and texture data, and the data obtained in the course of drilling and production. The final ana...

Geochemistry and Carbon Isotope Characteristics of Associated Gases From Oilfields in the Nw Greater Caucasus, Russia

“…3a). A number of oil and gas fields in this area produce from sandstone reservoirs in the Middle Miocene succession (Chokrakian: Derduga, 2010).…”

Controversial Issues of Hydrocarbon Field Formation and the Role of Geomagnetic Fields

“…The reservoir fluids move from the highest pressure areas to the lowest ones along the path of least resistance. Such pathways can be vertical disjunctive faults in the sedimentary cover [63][64][65][66]. Following this, the zones near faults may be the source of discrete geomagnetic fields, which in turn may influence the petroleum generation processes due to the spin magnetic effects during the transformation of organic matter.…”