Cluster and dual-lateral drilling technologies optimize Russian well production

Ravil Gabdullinovich Salikhov
JSC Lukoil-Burenie
Samara
Evgeny Fedyorovich Dubrovin, Vladimir Vladimirovich Sledkov
Lukoil Oil Co.
Moscow

Russia's largest drilling contractor, JSC Lukoil-Burenie, uses cluster drilling to improve rig mobilization and dual-lateral drilling to increase production.

The company was created in 1995 from organizations formerly part of Lukoil Oil Co. In 1996, Lukoil-Burenie drilled 1,220,000 m (4,003,000 ft), including 1,029,000 m of production and 191,000 m of exploratory drilling. A total of 616 wells were drilled for customers.

The company's headquarters is in Samara (Fig. 1 [180,840 bytes]). It has two affiliates: the West Siberian branch in Kogalym, and the Perm branch in Polazna. In addition, it has two employee training centers. In 1997, Lukoil-Burenie plans to acquire the Volgograd drilling enterprises.

Lukoil-Burenie has 49 drilling rigs with capacities from 75 to 320 metric tons. The company also has well plugging equipment, trucks, tractors, and cranes used in well site preparation and rig erection. Kremco mobile drilling rigs are utilized for drilling, workover operations, and drilling of secondary well bores (dual-laterals) in existing wells.

The company develops customer relations on a turnkey contractual basis. Among its customers are Lukoil's oil producing enterprises, as well as joint ventures with such companies as Soco, Agip S.P.A., and Deminex GMBH.

West Siberian cluster drilling

Lukoil-Burenie operations occur mostly in West Siberia, concentrated in 22 fields within the vicinity of Kogalym, Langepas, and Urai. This region is known for its swampy terrain, long and cold winters, and vast distances. In this environment, the cluster-well drilling method is used because it expedites the rig mobilization process. Fig. 2 [32,064 bytes] shows a typical cluster well-pad design.

With this method, linear patterns of predefined well locations are sequentially drilled using a rail system that moves the rigs from location to location. The BU3000 EUK drilling rig is specially designed for use on these locations (Fig. 3 [54,292 bytes]). These rigs can be broken down into modules for relocation. Rigging-down and rigging-up normally takes 2-3 hr.

During the move, hydraulic pushers jack the platform-mounted equipment along the tracks in 1.5 m strokes. Standby diesel generators power the necessary equipment while in transit. Once on location, hydraulic jacks center and level the derrick and drawworks.

While drilling, a 6-kv transmission line provides electricity to ac motors for main power. Mud pumps are equipped with variable-speed drives and bit weight is automatically controlled.

Casing program

Casing in West Siberian wells normally consists of setting 245 mm (9.65 in.) surface casing at 700 m (2,297 ft), and 146 mm (5.75 in.) production casing at 2,800 m (9,186 ft). Wells are cemented up to the wellhead.

Under certain geological conditions, the lower casing-string section is equipped with a filter screen. Cementing baskets are used for cementing operations in horizontal wells.

Production strings are often run and cemented above the producing formation. The formation is then drilled out and slotted screens are run in the well bore. Annular packers are customarily installed in fields with oil/water contacts.

Directional drilling

The wells are directionally deviated with departures of 1,500 m and true vertical depths of 2,600 m. Well patterns and borehole spatial orientations for a cluster-well system are shown in Fig. 4 [42,992 bytes].

The drilling process uses downhole turbine motors, including the speed-reducer type, as well as screw-type downhole motors. The average penetration rate is 22.9 m/hr (75 ft/hr) and the footage/bit varies from 175 to 750 m (574-2,461 ft), depending on depth and rock properties.

Several types of bottomhole assembly are utilized for directional control. Turbodrilling deflectors with special subs and deviated axes (bent subs) are used for increasing inclination and azimuth control. Special coaxial tools, including centralizers and calibrators, are utilized for borehole directional control. Borehole spatial parameters are controlled with continuous-action, downhole telemetry systems using electromagnetic communications. In addition, inclinometers are used for intermittent measurements.

Mud program

Because the formations in West Siberia are not prone to significant hole problems, mud programs are directed toward cost minimization and the prevention of formation damage into the production zone. Acrylic polymers provide rheological control, wall-building properties, and borehole stabilization above the producing formation. Drilling below the top set casing is performed with minimal clay or clay-less muds treated with polysaccharides.

Use of various starchy chemicals, carboxymethylcellulose, and oxyethylated variations depend on the specific drilling conditions. Phosphonic complexones, potassium chloride, and metasilicates are utilized as inhibiting additives.

The rigs are being retrofitted with contemporary technology and transition to a four-step treatment system including the use of centrifuges is under way. In some cases when there are abnormal environmental requirements, mud treatment systems are equipped with additional chemical enhancements and flocculation.

In 1997, Lukoil-Burenie and Derrick Equipment Co. started using pitless technology for drilling in natural preserves and priority land use areas. This technology uses mechanical and chemical means to separate solid waste from the drilling fluid resulting in clean water as an end product.

The West Siberian branch has drilled three horizontal wells, two in the Kogalym area and one in the Langepas area using the latest technology. The maximum horizontal reach in the producing zone was 350 m and flowing production rates increased by 320%. The company plans to drill three more horizontal wells.

Perm region drilling programs

Lukoil-Burenie's Perm branch also uses the cluster-well drilling method. This region has its own distinct features. In the northern part, hydrocarbon accumulations are overlain by thick salt formations of halite, carnallite, and sylvinite, comprising some of the thickest salt deposits in the world. There are no salt formations, however, in the central and southern areas of the Perm region. The producing formations in this region are found at shallower depths characterized by highly abrasive rocks.

There are complications associated with sloughing shales, lost-circulation into karst formations, as well as multiple, high-permeability zones that contain highly saline, hydrogen-sulfide saturated formation waters.

Because of the various geological conditions in the Perm region, the producing formations have a wide range of depths, beginning with 600 m in the south to 2,700 to the north.

Perm casing and mud program

A typical casing program for the Perm region consists of setting 324 mm (12.75 in.) surface casing at 180 m (591 ft), 245 mm (9.64 in.) intermediate casing at 900 m (2,953 ft), and 146 mm (5.75 in.) production casing at 2,300 m (7,546 ft).

Highly efficient, clay-less polymer, polymer-brine, and brine drilling muds are used in over 50% of the wells. Special chlorine magnesium-phosphate muds are utilized for drilling through salt deposits. For borehole isolation from salt deposits, intermediate casing strings are cemented with oxychloride (magnesium) and oxysulphate cements.

For drilling into the producing formations, clayless and low-clay muds treated with polysaccharides and surfactants are used. These muds are weighted with a carbonaceous weighting agent for drilling in abnormally high-pressured formations. Close attention is paid to the strengthening and increasing of the hydraulic sealing properties in the near-borehole zone during the primary drilling, and the use of polymer and clay destructors while drilling the dual-lateral sections.

The Perm branch is also experienced in drilling horizontal wells. Seven wells were drilled and completed by the end of 1996. There are plans to continue drilling more horizontal wells in 1997-1998 and to increase the scope of work in this area.

Dual laterals

It is important for all Lukoil producing enterprises to place idle, shut-in wells back into production and to increase well-pattern density. The most efficient solution to this is to reenter existing wells and drill secondary boreholes.

About 10 dual-lateral wells have been drilled in West Siberia, and there are plans to drill at least 250 more. Of these 250, 150 wells will be vertically displaced by 450 m with 150 m of horizontal reach.

In addition, 32 dual-lateral wells were drilled in the Perm region between 1995 and 1996. In 1997, Lukoil-Burenie plans are to increase the scope of this work to 20 wells annually. Sidetracking and drilling dual-lateral operations are based on domestically developed technologies.

Fig. 5 [59,113 bytes] shows a casing window-cutting bottomhole assembly. Its main feature is a telescopic casing cutter shown in Fig. 6 [61,933 bytes]. As a rule, sidetracking is done by cutting out a portion of casing, up to 8 m long, using a rotor mill. In some cases, a window is made using a whipstock and reamer mills.

Orientation of the dual-lateral is accomplished with downhole wire line telemetry. The anchor uses a liner with a packer element run on a disconnecting collar.

Localized hydraulic fracturing is used to optimize production and reopen abandoned wells. After treatment, flow rates have increased by 340-600%. Thermal and pressure treatments of bottom-hole zones are used for secondary well stimulation in the Perm region, with flow rates increasing by 130% after treatment.

Balanced drilling

In 1997, the West Siberian branch will start drilling six experimental wells using pressure-equilibrium drilling technology (balanced drilling), where the hydrostatic pressure is maintained at formation pressure. The system will utilize blowout preventers and Shaffer degassing system. This is viewed as a promising technology, considering that there are so many low-permeability reservoirs in West Siberia with formation pressures close to hydrostatic.

The lower Volga producing formations, currently under development by the Volgograd drilling companies, normally consist of carbonaceous reef rocks such as finely and heavily fractured limestones and dolomites. The characteristic features of these formations are tectonic faults with formation pressure gradients greater at the top than at the bottom.

Several methods are available for drilling under these regimes including mud aeration. In doing so, two rotating blowout preventers are installed at the wellhead and an air compressor is connected to a manifold. This technology has been successfully applied to over 50 wells.

In order to prevent hydraulic formation fracturing, the casing is filled with over-lightened plugging fluids filled with microscopic hollow glass spheres 25-30 ? in diameter.

The Volgograd drilling companies have drilled and completed 11 horizontal wells with up to 450 m horizontal reach within producing formations 412 m thick, at depths of 700 m.

Training

The Lukoil-Burenie training centers are geared for training workers, engineers, and technicians who have various levels of experience in operations and safety. Training centers include operating mock-ups of drilling rigs, actual drilling equipment, mud motors, and drill bits.

Mud and cement labs are equipped for comprehensive analysis of fluid properties, chemical treatment, and evaluation of chemical and material properties. To enhance skills, practical lessons in servicing pipe and mud motor repair under actual production environments are offered together with training on models.

The most effective form of employee training includes actual sessions conducted on a Uralmash 3000/200 DGU, located at the Birsk training facility.

Currently, there is a need for upgrading the training centers with installation of the state-of-art training models, new guideline materials, and teaching and testing software. This will increase the efficiency of these centers and make it possible to set up a system of annual, short-term training courses for familiarizing the engineering and technical personnel with the latest technological advances in well drilling, as well as to support and enhance professional skills and qualifications.

The Authors

Ravil Gabdullinovich Salikhov has been the general director for JSC Lukoil-Burenie since 1978. He graduated from the Tyumen Industrial Institute specializing in oil and gas drilling in 1977. Immediately after graduation, he began working as an assistant driller. Salikhov has also studied in Azerbaijan, France, Italy, and the U.S.

Evgeny Fedorovich Dubrovin is the department director for Lukoil Oil Co. He graduated from the Kuebishev Polytechnical Institute as a mining engineer. Dubrovin has 25 years, experience in drilling of which 10 years were spent in West Siberia.

Vladimir Vladimirovich Sledkov is the department chief for Lukoil Oil Co. He graduated from the Moscow Academy of Oil and Gas in 1977. He was involved in the ultra-deep Kolsky well that was drilled to 12,263 m (40,233 ft). Sledkov has a candidacy degree (doctorate) in technical sciences. He is also an author of 20 science articles and has 10 patents.