Cand.Tech.Sci. Ponomareva M.V., Blochitsyna A., Nikitina A., Ponomareva Ye.

Karaganda State Technical University. Kazakhstan

Optimization of geophysical research

in Kotyrtas deposit’s wells

Kotyrtas deposit is situated in the south-east part of Caspian Depression in the Republic of Kazakhstan. Base wells are exposed by the complex of geophysical methods. Main criterias for selection of base wells are maximum completion of producing reservoir, production test, characteristic of cut by core and uniform well spacing. Researches were conducted both open hole and cased-hole by oilfield service companies.

Primary objectives of geophysical well logging on Kotyrtas deposit were geologic-geophysical vertical exploration of well, selection and correlation of geophysical log markers, lithological layering, reservoir limit test, stratification and areal convergence of reserves, allocation of collector layers, estimation of reservoir saturation type, quantitative determination of net thickness collector layers` reservoir properties, well integrity study.

According on results of prospecting, development and exploitation drilling it is found that a productive stratum is dated to Middle Trias. The productive formations were penetrated by using drilling mud which is created by thoroughly mixing water with clay to a desired consistency.

Drilling mud electrical resistivity was measured by a borehole resistivity meter in the process of micrologging and lateral logging curves matching plotted against thick layer of clay with bilayered master curve. Nonfilterable drilling mud was used during the drilling of several wells. It limited using other modifications of resistivity method except induction logging.

Recording of geophysical well logging curves was performed by logging laboratories with digital recorder.

Logging in prospecting and development wells was conducted in 2-3 cycles according to completion of formation. Logging in exploitation wells was conducted in 1 cycle after completion of objective horizon`s formation. Geophysical researches in wells included general exploration on well bore in 1:500 scale and detailed exploration of producing intervals in 1:200 scale.

Basic logging suite in prospecting and development wells (1:200, 1:500 scale) included followed methods: standard logging by inverted (B0.5A2M, N0.25M2.25A) and standard (M2A0.5B) devices with one-time SP, caliper, acoustic logging, inclinometry, geological-technical study, seven-electrode lateral log with different transmission distance aiming to identification of resistivity radial gradient and laterlog diagrams quality control. Curves recording in several wells was conducted by 4L and 8L lateral logging.

Radiation logging included gamma ray and neutron-gamma ray curves all over the vertical exploration in wells.

Lateral logging, micro loging, caliper logging and radiation logging were perfomed in 1:200 scale from surface casing to bottom hole in the beginning of prospecting drilling.

In exploitation wells general researches in 1:500 scale include: standard logging by inverted and standard devices with one-time SP, caliper and radiation logging.

Detailed exploration of producing intervals in 1:200 scale includes previously mentioned methods and lateral logging sounding, lateral logging, induction logging and micro logging sounding.

Inclinometry, cement top location and cementing control were conducted to explore technical conditions of wells

Inclinometry was used for hole accuracy control. Cementing quality control and cement top location were defined with using acoustic cement bond log and thermometry.

Picture 1 - Geological parameters of supporting layers

The estimation of geophysical data quality was realized in all the working wells. Correction of using curves was made in case of need. Totally, completeness and quality of achieved logging data allow to allocate reservoirs and to estimate its filtration-volumetric characteristics and oil saturation.

Provided that quality of measurement is fine researches conducted in wells allow to solve primary objectives. Controlling-interpretation groups of production department regulated calibration and curves repeatability in sealing intervals.

Final quality control of geophysical data was carried out in process of complex interpretation by static analysis of geophysical data in supporting layer of workable well. Layers of salt and anhydrite are counted as supporting layers. Geological parameters are given at picture 1.