Физика/5.Геофизика

C.t.s. Ponomareva M.V., c.t.s. Pak D.Yu., Vdovkina D.I., Nurtaza Zh.

Karaganda State Technical University. Kazakhstan

Reservoir current saturation at Kumkol deposit

according to nano-electrical logging date

The tasks faced by subsoil users are to maximize oil recovery efficiency and to involve undeveloped reserves to production. To identify such undeveloped reserves neutron methods such as C/O logging are used, however, these methods have significant limitations: shallow radius of investigation, inability to survey perforated intervals, interpretation complexity (measurement data have to include multiple influence factors, rock porosity, shale and carbonate content). Therefore, the innovative method of nano-electrical logging (NEL) which allows an evaluation of reservoir current saturation through cased walls comes forth as a relevant and efficient method.

Nano-electrical logging is an electrical well logging method which provides continuous measurement data. NEL is used to obtain electrical properties of rocks located outside borehole casing filled with any fluid. Borehole casing does not affect the measurements. Owing to the large radius of investigation (starting from 2 meters) NEL provides completely new capabilities in terms of oil and gas producing horizons survey. NEL can be used to:

– determine true specific formation resistivity from 1 to 100 Om-m with measurement error ±2%;

– identify unknown or uninvolved in production oil and gas horizons;

– determine and ascertain water/oil and gas/oil contact locations;

– determine current oil and gas content of horizons;

– determine formation porosity.

Analysis of NEL features involved field trials and interpretation of the acquired geophysical data using electrical logging equipment through the casing to evaluate current saturation of Cretaceous and Jurassic producing horizons at Kumkol deposit. Kumkol deposit as an administrative unit is located in Dzhezdinskiy Destrict, Karaganda Region, Republic of Kazakhstan. The distance to Kyzylorda, Regional Center, is 180 km. Geographically the deposit is located in the southern part of Turgai depression. Kumkol deposit includes Mesozoic and Cenozoic deposits underlying Early Proterozoic basin. Kumkol deposit consists of terrigenous rocks: sandstones, shales, silt stone, and argilletes.

Geophysical surveys were conducted for two wells (different results obtained) at survey interval of:

Well X1: survey interval: 1120–1114m (in increments of 0.5m), 1114–1090m (0.2), 1090–1085m (0.5), number of measurement points – 142.

Well X2: survey interval: 1288.4–1235m (0.2 m), 1157–1152m (1.0m), number of measurement points – 273.

The NEL interpretation results revealed:

1. Behind pipe interval (J-I, J-II horizons).

2. Perforated interval (J-III) located immediately at the bottom hole zone and used as supply interval.

3. Rt depth shift (1.6m) and good correlation (when adjusted to guide bed) with open hole logs.

4. Water encroachment of J-I horizon.

The complex interpretation results are shown at the table, figure 1.

The conducted field trials revealed that electrical logging through casing stands out among other methods used to evaluate current saturation (C/O logging, TDT log, pulsed gamma-ray logging):

1. Greater depth of investigation which allows obtaining results for reservoirs with inactive invasion zone.

2. Availability of “comparison” logs (there is an archive of open hole logs completed at the drilling stage available for the majority of wells regardless of their age). This enables visual identification of the changes that have taken place since putting the wells into operation.

3. Relative easiness of interpretation (fewer interim calculation factors between the measured parameter and remaining saturation) which increases its adequacy.

Figure 1 – Evaluation of current oil saturation using nano-electrical logging

References:

1. Itenberg S.S., Interpretation of well logging results.–M.: Nedra, 1998

2. Catalog Western Atlas International. М.: 1991