Some Issues in Reducing the Cost of Prospecting and Exploration Drilling for Oil and Gas in Western Siberia

V. I. Ioppa, S. Ya. Tsyba

(Presented by the scientific seminar of the Department of Industrial Economics and Enterprise Organization)

Prospecting and exploration drilling has a number of specific features that distinguish the organization of these operations from development drilling, especially in Western Siberia with its difficult natural and climatic conditions. Drilling operations here are carried out almost everywhere under conditions of great remoteness from population centers and supply bases, far from transport routes, in hard-to-reach and uninhabited areas. For much of the year, most drilling rigs are inaccessible to ground transport, and the only means of communication is aviation. This complicates the uninterrupted supply of materials to drilling rigs and the delivery of service personnel, reduces the effectiveness of engineering supervision over the process of drilling wells, and causes prolonged downtime of drilling rigs because they cannot be transported.

However, the technique used in conducting these operations, the drilling methods, equipment, and well designs have been mechanically transferred from development drilling, which increases the cost of oil-prospecting work and to a significant extent contributes to the sharp lag of the technical and economic indicators of prospecting and exploration drilling behind those of development drilling (Table 1).

In Western Siberia—one of the most rapidly developing regions of the oil and gas production industry—despite the improvement of the drilling equipment being used, drilling techniques and technology, and the increase in commercial drilling speeds, a noticeable tendency has emerged toward deterioration of the principal technical and economic indicator: the cost per meter of deep-well penetration (Table 2).

The difference between the indicators of prospecting and exploration drilling and development drilling, and the growth in the cost per meter of deep-well penetration, are explained both by objective causes (an increase in average well depths, the remoteness of work areas from supply bases, etc.) and by the fact that oil-prospecting work is carried out without taking into account the specific features of prospecting and exploration drilling under the conditions of Western Siberia. It must not be allowed that the further expansion of oil-prospecting work proceed solely through increased capital investment. Therefore, reducing the cost of constructing deep wells, as the most capital-intensive type of prospecting and exploration work for oil and gas, is of primary importance in increasing the economic efficiency of geological exploration work.

Table 1

Main indicators of prospecting-exploration and development drilling for oil and gas in Western Siberia in 1970

Table 2

Average well depths and cost per meter of prospecting-exploration drilling penetration in Western Siberia in 1966–1970

The main directions that make it possible to solve this problem include:

1. Reducing transportation costs, which in Western Siberia amount to 35–50% of the total costs of drilling wells [3, 5].

2. Increasing the productivity of drilling rigs.

The large share of transportation costs is due to the following factors: a) difficult road conditions, which make it necessary to use expensive all-terrain equipment; b) the high cost of road construction; c) the great weight of drilling rigs and materials; for example, the BU-125BD drilling rig weighs 330 tons, while the total weight of the set of equipment and materials for drilling one well is on the order of 800 tons; d) long haulage distances. Thus, in the Tomsk Territorial Geological Administration (TTGU), the average transportation distance for drilling rigs in 1970 was 106 km. Such distances are typical for all districts of Western Siberia.

As we can see, a sharp reduction in the weight of drilling rigs and an increase in their mobility and transportability are the primary task in reducing the cost of transportation.

One way of reducing the weight of drilling rigs is to improve the design of equipment components, lighten their weight through the use of light-alloy materials, replace housings with welded ones, and select the most advanced kinematics for the drilling rig. As foreign experience shows, the use of a direct-current diesel-electric drive with an ideal operating characteristic ensures minimum weight and good transportability and assemblability of drilling rigs [1, 2].

In recent years abroad, the number of direct-current diesel-electric rigs has been growing rapidly, especially in hard-to-reach areas. Thus, from 1958 to 1968 in Canada and the United States the number of rigs with diesel-electric drive increased from 49 to 279 and amounted to 9% of the total number of rigs; and in Cook Inlet, Alaska, in 1968, out of 20 rigs, 16 had diesel-electric drive [2, 5].

An important factor in reducing the weight not only of drilling rigs but also of the materials used in drilling is the drilling of exploratory wells of reduced diameter.

It is known that in development drilling the well design (and, consequently, the class of the drilling rig used and its weight) is determined mainly by the requirements for rational exploitation of the field.

Proceeding from these requirements, the final diameter of development wells in Western Siberia has been adopted as 190 mm.

The requirements for prospecting wells are entirely different: the chief aim is to obtain geological information. These requirements are fully met by wells of a diameter reduced in comparison with the accepted one (190 mm), which make it possible to carry out in them the entire complex of research operations, obtain full-value geological material, and solve questions of prospecting and exploration of fields.

Consequently, from the geological point of view, drilling small-diameter wells cannot raise objections.

From the technical point of view, drilling small-diameter wells is possible with sufficiently high technical-and-economic indices and makes it possible to:

a) lighten the drilling and casing strings and, consequently, use a lighter drilling rig;

b) reduce the specific energy costs of drilling a well and reduce the consumption of fuels and lubricants;

c) reduce the labor intensity and duration of construction and installation work;

d) reduce the consumption of materials (pipes, hoisting cable, cement, etc.) for drilling the well;

e) reduce the costs of transporting the drilling rig and materials;

f) reduce expenditures for the acquisition of drilling rigs and depreciation charges.

Experimental work on drilling wells with a diameter of 161 mm, carried out in 1966–1967 in Tomsk Oblast [3, 4], shows that the equipment and tools currently produced in series already make it possible, with great effect, to drill wells of reduced diameter. As a result, for each well the cost of materials will decrease by more than 6 thousand rubles (Table 3).

Table 3

Consumption of basic materials per well of the adopted design (190–146 mm) and the experimental design (161–114 mm)

Note. Well depth 2800 m. Conductor setting depth 400 m.

Taking into account that the cost of transporting most materials is twice their selling price, the economic effect in TTGU alone will amount to half a million rubles per year.

As noted above, the impossibility of transporting drilling rigs by surface transport in the spring–autumn period leads to a low utilization factor of the equipment, which remains idle for a long time while awaiting winter roads. In this connection, the need for it is almost twice as great as for the same drilling volumes in areas with a year-round transport network.

In addition to large expenditures on depreciation charges for idle expensive equipment, the evaluation of new

areas, the pace of prospecting and exploration for oil and gas fields slows down.

As the actual data for the TTGU show, with an increase in the percentage of prospecting drilling, the productivity of drilling rigs, despite the growth in drilling speeds, decreases (Fig. 1), mainly because of the time spent on their transportation and on downtime. The average productivity of drilling rigs in 1966–1970 was 3430 m per rig per year, with an average well depth of 2443 m.

Fig. 1. Productivity of drilling rigs, percentage of prospecting drilling, and average well depths for the Tomsk Territorial Geological Administration in 1966–1970.

I — percentage of prospecting drilling
II — productivity of rigs, m
III — average well depth, m

Therefore, one of the important ways to increase the productivity of drilling rigs and, consequently, to reduce the cost of drilling work is, above all, to reduce the time for such stages of rig turnover as transportation and downtime, which can be achieved through the use of aviation.

Calculations show that in the TTGU alone, the use of helicopters for transporting BU-80 drilling rigs would make it possible to significantly increase their productivity and, by reducing the share of depreciation charges, obtain annual savings of more than half a million rubles [3]. However, helicopters have a number of shortcomings, the main ones ...

among which are the high cost of flight hours and limited load-carrying capacity.

The data presented make it possible to draw the following conclusions:

1. Improving the technical-and-economic indicators of prospecting and exploration drilling requires its broad and comprehensive specialization, taking into account the specific requirements of prospecting and exploration work, as well as natural-climatic and geological conditions.

2. The main directions for reducing the cost and, consequently, increasing the economic efficiency of prospecting and exploration work for oil and gas are drilling small-diameter wells and increasing the productivity of drilling rigs through the use of air transport.

3. On the basis of light drilling rigs produced in series, as the first stage in the transition to lighter well designs, it is necessary to resume pilot-industrial work on drilling wells with bits of 161 mm diameter, with the running of a 114 mm production casing.

REFERENCES

1. E. E. Roshal, Yu. A. Amelin. Increasing the Mobility of Drilling Rigs for Deep Exploration Drilling Abroad. Review. Moscow, VIEMS, 1971.

2. M. M. Khushpulyan et al. The Present State of Power Units, Drives in Drilling, and Criteria for Their Selection. Review of Foreign Literature. Moscow, VNIIOENG, 1971.

3. G. R. Podobin, S. Ya. Tsyba, V. I. Ioppa. Issues in Increasing the Technical-and-Economic Efficiency of Prospecting and Exploration Drilling for Oil and Gas in Tomsk Oblast. Proceedings of TPI, No. 269, Tomsk University Press, 1973.

4. N. N. Kokhmanskaya et al. Drilling Operations in Alaska. Review of Foreign Literature. Moscow, VNIIOENG, 1972.

5. Z. F. Shpakova. Features of Deep Exploration Drilling under the Conditions of Western Siberia.—Neft i gaz, 1971, No. 14.