Issues of Improving the Technical and Economic Efficiency of Exploratory Drilling for Oil and Gas in Tomsk Oblast

G. A. Podobin, S. Ya. Tsyba, V. I. Ioppa

(Presented by the scientific seminar of the Department of Economics)

To provide the rapidly developing oil-producing industry of Western Siberia with oil and gas reserves, it will be necessary to increase substantially the volume of petroleum exploration work and, above all, deep drilling. At the same time, it must not be allowed that the growth of reserves proceed at the cost of a sharp rise in capital investments, as has been the case up to the present time.

The most capital-intensive type of exploratory work for oil and gas is the construction of deep wells, and reducing their cost will play a primary role in increasing the economic efficiency of geological exploration work.

The main reserve for reducing the cost of drilling work is considered to be an increase in the commercial rate of penetration. However, in Western Siberia, owing to its natural features, this is a necessary but insufficient condition for sharply reducing the cost of drilling. This is confirmed by calculated and actual data (Table 1) for the Tomsk Territorial Geological Administration (TTGU). Obviously, in order to ensure significant rates of reduction in the cost of drilling work, it is necessary to reduce both the costs that depend on time (rate) and the costs that depend on the volume of drilling.

As is known, one of the main directions of modern scientific and technological progress is the reduction of the material intensity of a unit of output. In petroleum exploration work in areas with difficult natural conditions, to which Western Siberia—and, in particular, Tomsk Oblast—belongs, the main ways of reducing the material intensity per unit of final output, the well, are the use of lighter drilling rigs and the simplification and lightening of well designs. Throughout the entire period of petroleum exploration work in the territory of Tomsk Oblast, well designs have gradually been improved. Thus, a transition was made to a single-string design and to the predominant use of 114 mm production casing strings. As a result, the consumption of casing pipe per meter of penetration was significantly reduced. However, this progressive undertaking did not receive its logical completion: wells of lightweight design are drilled by drilling rigs of the same load capacity as in the initial period of exploration work; specific energy expenditures, consumption of cement and other materials still remain high. As a result of the use of heavy-

...drilling rigs and the large consumption of materials, freight haulage accounts for 35% of the cost of well construction and, under conditions of taiga swampy terrain that preclude the rapid maneuvering of mechanized equipment, is the most pressing problem.

Since, in addition to drivers and riggers, derrick-assembly workers, testers, and drillers are also involved in transporting freight, it may be assumed, without great error, that the number of workers engaged in primary production and in freight haulage is the same. To one degree or another, practically the entire shop engineering and technical staff is concerned with issues of freight transportation.

Table 1

Principal indicators of oil and gas prospecting-and-exploration drilling at TTGU for 1966–1970

Calculations show that, with the well design currently adopted (final diameter 190 mm), their drilling can be carried out by lighter BU-80BrD drilling rigs. With the use of drill pipes made of light alloys, these rigs can drill wells to a depth of 3550 m, which, at the existing rates of increase in their average depths (Table 1), will ensure the solution of geological tasks in the next 5–6 years.

Replacing the Uralmash-3D and BU-125BD drilling rigs, whose cost and weight differ only slightly when appropriately equipped, with the lighter and more transportable BU-80BrD will make it possible to:

1) reduce the rental cost of drilling equipment owing to its lower initial cost and an increase in the utilization coefficient by transporting drilling rigs by helicopter;

2) shorten the duration and reduce the cost of derrick-assembly work;

3) reduce expenditures for transporting equipment and materials;

4) lower operating costs;

Table 2

Approximate calculation of the cost of rental and transportation of drilling rigs

thousand rubles:

The approximate calculation (Table 2) shows that merely by reducing the rental cost of small-block BU-80 BrD rigs for TTGU, the cost of work can be reduced by about 1 million rubles per year.

In hard-to-reach areas with difficult road conditions, drilling small-diameter wells is very promising [1].

By the present time, in our country and abroad, a certain amount of experience has been accumulated in drilling deep small-diameter wells, indicating the great potential of this approach in reducing the cost of geological exploration for oil and gas [1, 2, 3].

It would seem that the expediency of drilling small-diameter prospecting and exploration wells in Western Siberia is obvious. What, then, prevents the implementation of this important reserve for reducing the cost of oil-prospecting work? One of the main problems is that domestic industry produces an insufficient number of bits,

turbodrills and small-diameter drill pipes that ensure the attainment of the same indicators as when drilling wells of normal diameter. But this does not mean that raising the issue of a transition to drilling small-diameter wells is premature. As the experience of switching to drilling the main bore of wells with 190 mm bits shows, the pace at which new equipment is improved depends in many respects on the scale of its application. Obviously, the further development of research and design work, as well as improvement of the manufacturing technology for small-diameter drill pipes, turbodrills, and bits, will be directly dependent on the demands of production and on the accumulation of experience in their application.

However, the main reason hindering the transition to the use of light drilling rigs is that the designs of exploratory—and often also prospecting—wells are developed in accordance with the requirements of their possible long-term operation. There are serious doubts as to the relative validity of the effort to meet these requirements. Of the total number of prospecting and exploratory wells, only 30% prove productive. Moreover, far from all of them are subsequently put into operation. The latter is explained by the following main reasons:

1. In prospecting and exploratory wells, after the study of productive formations, the overlying promising horizons are often tested.

2. Oil exploration workers, not having a sufficient amount of data on the oil-and-gas potential of the section, cannot take into account all operating requirements; and under taiga conditions and in impassable swamps they are unable to concentrate at the drilling site the technical resources needed for high-quality isolation of formations.

3. In areas remote from oil fields, exploratory wells remain shut in for a long time, which has a very substantial effect on their durability during operation. As a result, many exploratory wells do not meet operating requirements.

On the territory of Tomsk Oblast about 400 wells have been drilled, of which no more than 50 are suitable for operation. If one takes into account the high efficiency of exploration over the past period of work, it may be assumed that, overall, no more than 10% of prospecting and exploratory wells will be operated. Since the cost of an exploratory well is on average 2–3 times higher than that of a production well [1], it is clear that reducing the costs of prospecting and exploratory work by only 5% through drilling small-diameter wells will make it possible to save funds for the construction of full-fledged production wells in place of exploratory wells not transferred to operation. The potential possibilities for reducing costs by lightening and simplifying well designs and drilling them with light drilling rigs are much greater [1]. This is confirmed by experimental work on drilling small-diameter wells with the BU-50 Br1M drilling rig at the Sovetskoye oil field.

Table 3 presents a comparison of the main technical and economic indicators for experimental small-diameter wells and the best normal-diameter wells drilled at the Sovetskoye field. The experimental wells were drilled by the rotary method using ordinary 89 mm drill pipes and using 114 mm drill pipes as the bottom-hole assembly. In the process, six types of small-diameter bits and the Nedra core-barrel assembly were tested. Consequently, the drilling regimes were far from optimal. To this must be added the costs associated with mastering, for the first time, the drilling-control system used in the drilling administration.

Table 3

* The higher costs are due to expenditures on air transport.

BU-50 Br1M rigs. Nevertheless, the technical rate of drilling small-diameter wells is only 25% lower than that of wells on which record performance was achieved, but 1.4 times higher than the field average.

As can be seen from Table 3, with a commercial rate 1.4–1.5 times lower, the cost of small-diameter wells is lower than the cost of normal-diameter wells in the drilling of which the best performance was achieved. Estimates carried out with allowance for the data obtained in the course of experimental work indicate that, in the worst case, the duration of drilling small-diameter wells will be only 10–15% greater, while the cost will be 25–30% lower than that of normal-diameter wells. The data presented make it possible to draw the following conclusions.

Under the conditions of Tomsk Oblast, for drilling normal-diameter wells (190 mm), it is most advantageous to use BU-80 BrD drilling rigs.

A highly promising direction for reducing the cost of oil-prospecting work is the drilling of deep small-diameter wells with light drilling rigs. It is necessary to resume pilot-industrial work on drilling wells with 161 mm bits and, in the near future, to carry out the transition to the new well design in one of the expeditions of TTGU, which has the largest volume of prospecting drilling.

REFERENCES

1. S. I. Kuvykin, N. I. Shatsov et al. Drilling of Small-Diameter Oil and Gas Wells. Moscow, “Nedra,” 1967.

2. S. I. Kuvykin. Drilling of Small-Diameter Exploratory Wells. Gostoptekhizdat, 1967.

3. M. A. Aleksandrov. Economics of Drilling Wells with Reduced-Diameter Bits. Moscow, “Nedra,” 1968.

4. V. I. Belov, V. M. Karpov, N. E. Shevaldin. Features of Drilling Oil and Gas Wells in Tyumen Oblast. Moscow, “Nedra,” 1966.