TNK-Uvat tested a mini-pilot hole drilling technology in its Ust-Teguss field to improve economic efficiency and reduce horizontal well drilling time. As a result, well construction time has been cut by 30 percent – from 46 days to 30 days.
One of the key fields in Uvat, Ust-Teguss is now in its first stage of commercial development, which involves large scope of development drilling in the field. As the J2 formation has very good reservoir properties (permeability of 150 mD, porosity of 0.19, gross thickness of 17 m, pay thickness of 10 m, good continuity, no wedgingout or shaling-out zones), horizontal drilling technology is widely used in Ust-Teguss. As of January 1, 2012, 23 horizontal wells were drilled in the field with the average initial flow rate of 350 tpd and the average length of horizontal section of about 600 m.
Initially, horizontal development wells in Pads #1 and #2 were drilled using conventional technology, with a pilot hole of 220 mm in diameter (Fig. 1), because of the high uncertainty about estimated structural surface, net pay thicknesses and reservoir properties of the J2 formation, which is the main productive horizon of the Tyumen suite. Verification of J2 subsurface parameters through drilling of a pilot hole allowed for directing the horizontal section through the best reservoir interval thus minimizing risks. This technology proved its worth but it took at least 45 days to drill one horizontal well with a pilot hole while its cost was almost as much as of two directional wells.
In terms of technology, all parameters and characteristics of the horizontal well drilling with a pilot hole were optimal and therefore, it was not possible to significantly reduce drilling time and cost. However, TNK-Uvat was determined to find a way to improve horizontal well drilling efficiency to reduce drilling time and bring forward start-up dates. In 2011, the team tested horizontal well drilling technology with a minipilot hole (152.4 mm), which goes without drilling of the main pilot hole, setting of abandonment and shut-off bridge plugs, “kicking-off” and drilling of tangent section.
Mini-Pilot Hole Drilling
The mini-pilot hole drilling technology is effective and simple. First, a 220.7-millimeter tangent section is drilled through the water-bearing J1 horizon of the Vasyugan suite down to the productive J2 horizon but not penetrating it, and a 178-millimeter casing string is run in and cemented. After that, the productive target is penetrated with a 152.4-millimeter bit equipped with an LWD (logging-while-drilling) tool. Importantly, a “ledge” is to be made at the beginning of the mini-pilot hole, which can later be used for safe drilling of the main horizontal section and running-in of a 114-millimeter slotted liner (Fig. 2). The minipilot hole logging is used to verify the J2 structure and geology, update the geologic model and design the horizontal section trajectory.
There is also a horizontal well drilling technology with no pilot. However, drilling of a mini-pilot hole helps verify the subsurface structure, pay thickness and heterogeneity of the production target, and so geologists can design an optimal trajectory for the horizontal section: run it through the best reservoir zone and avoid shale and low permeability interlayers in J2 horizon.
Less Time – More Profit
The main purpose of drilling mini-pilot holes is to significantly reduce well construction time and drilling costs. This technology was for the first time used for drilling Wells #2062G, #2063G, #2080G and #2050G, Pad #3,Ust-Teguss (Fig. 3). As a result, the average drilling time was reduced by 16 days, or 35 percent, – from 46 days with a pilot hole down to 30 days with a mini-pilot hole (Fig. 4, 5). The four wells were drilled 50 days faster than they would have been drilled with a pilot hole and this success cut TNK-Uvat’s drilling costs for these wells by 153.7 mln rubles. These wells were also put on stream earlier, which generated incremental oil production of about 29,000 t in 2011 only.
To use the mini-pilot technology effectively, the drilling region has to be studied with exploration or development wells verifying the target horizon geology: structural surface, pay thickness and reservoir properties. For that purpose, the pad drilling design shall include at least one directional well, which will helps minimize horizontal section drilling risks.
That is why the availability of exploration wells and the sequence of drilling were considered when developing the 2012-2014 drilling program. In Uvat Eastern Hub, 15 mini-pilot hole horizontal wells are planned to be drilled in Ust-Teguss, which will reduce well construction time by a total of 210 days, cut average drilling costs by $1.28 mln per well (a total of $19.2 mln) and ensure incremental oil production of about 180,000 t.
The mini-pilot hole horizontal well drilling technology can be used for both horizontal wells and sidetracks in virtually all TNK-BP subsidiaries that operate fields of similar depositional and structural characteristics. It is obvious that it can help reduce drilling time and costs and produce thousands of tons of incremental oil thus raising the value of the Company’s assets.