Determination of petrophysical parameters of reservoirs in promising horizons and formations of the Bulla-Deniz field based on integrated well data (using Techlog software)

Abstract

The Bulla-Deniz field which is characterised by deep wells has not been fully explored despite its commissioning since 1975. Consequently, the intersection of the Productive Series (PS) deposits has been drilled to the top of the Kirmaky group. The deposits of the sub-Kirmaky and Gala formations have not been exposed in the field area. The Bulla-Deniz field is located in the northern portion of the oil-gas region of the Baku archipelago, which is part of the Azerbaijani sector of the Caspian Sea. The structure was investigated through a comprehensive geophysical exploration program which included mapping, structure-search and logging datas.

The Bulla-Deniz structure is described in these materials as an asymmetric brachyanticline, extending in a northwest-southeast direction. Its dimensions are given as 27×9 km along the roof of the VII horizon and up to 1400 m high. The Bulla-Deniz fold is further complicated by the presence of longitudinal and transverse tectonic faults, which divide it into a number of tectonic blocks. The northeastern wing is divided into six tectonic blocks by six transverse faults. Two transverse fractures are noted in the southwestern wing, which divides the wing into 3 blocks (A, B and C blocks). In the geological cross-section of the Bulla-Deniz field, the sediments of the PS, Agcagil and Quaternary periods were identified in wells. The presence of Miocene sediments, as evidenced by excavations in the cross-section of neighboring deposits, is beyond doubt. The Miocene sediments have not been subjected to drilling studies. In consideration of the area’s geological tectonic structure, it can be postulated that the sediments underlying the PS may start at with the Pont floor, which is estimated to be 150 to 200 m thick. The intersection of the PS sediments was exposed by drilling wells to the top of the Kirmaky formation. The Sub-Kirmaky and Gala formations were not subjected to field investigation. In accordance with the classification system utilized by the Absheron division, the VIII horizon is identified as the Kirmaky sandy formation. Two sand-siltstone layers are observed in the lower and upper portions of the horizon. The VII horizon is equivalent to the «Fasilah» formation, as defined by the Absheron division. It is primarily composed of sandstones. Horizon V (corresponding to horizons VIII-IX according to the Absheron division) was represented by alternating layers of thick sand, sandstone and shale. The oil and gas in the Bulla-Deniz field are located within the V, VII, and VIII horizons of the PS. However, since these horizons in the southwestern wing have not been accessed through wells, their oil and gas content remains unknown. From this point of view, important issues such as detailed study of the Bulla-Deniz field, evaluation of its horizons and strata in terms of productivity, determination of its petrophysical parameters and calculation of reserves are still valid today.

The article deals with the determination of petrophysical parameters of reservoirs, calculation of oil reserves and determination of oil-water contact using complex well logging data on promising horizons and reservoirs of the productive series of the Bulla-Deniz field.

To solve the problem, the Techlog software was used to study the total and effective porosity, clay content, permeability, oil and gas saturation and water saturation of reservoirs in perspective reservoirs in terms of productivity on the basis of integrated log data from 6 well sections of the Bulla-Deniz oil and gas condensate field characterised by deep wells. The total volume of oil by wells in blocks A and B, separated by faults, was calculated according to our parameters, intervals of oil-water contact were determined and correlation by reservoirs was made for wells belonging to each block.

The density logging data were used to calculate the values of total and effective porosity of reservoirs for each well section and to construct curves characterising variations of these parameters over the survey interval. Given that these parameters are dynamic parameters of reservoir layers, the intervals of reservoir layers along the section were determined using these curves.

In the course of the research work for each well section we investigated, using electric logging data and Techlog software, we determined the intervals of the oil-water contact, determined oil- and water saturation parameters and established curves of their variation by depth. The curves were used to determine the intervals of water-bearing and oil-bearing layers in the section. Determination of the oil-water contact is of scientific and practical importance in determining the nature of the boundaries of the oil and water zones in the reservoir and identifying watered productive layers.

In this article, using the average values of parameters determined in the Bulla-Deniz field, the oil volume for blocks A and B separated by the fault and the total oil volume for the studied area were also calculated.

As well as in the detailed determination of petrophysical parameters, in determining the relationship between them, in the more precise calculation of reserves at the fields.