Verkhnechonskoye: Reducing Horizontal Well Construction Times
The construction time of a horizontal well at the Verkhnechonskoye oil and gas condensate field has been significantly reduced thanks to drilling a 178-mm production casing interval in a single run using the QuadCombo logging suite.
The Verkhnechonskoye field keeps embracing optimization of well drilling and construction. To date, the average drilling time for a horizontal well is approx. 3 weeks (21-22 days). Most of the time is spent on drilling the 178-mm production casing interval with a 215.9-mm diameter, which takes 7-9 days on average, the drilling interval is from 1,600 to 2,400 meters, the final bottom hole target for the production casing is 2,200-3,200 m. Upon completion of the drilling, a wiper trip is performed using a bottom hole assembly (BHA) with a set of logging tools, including AZD/TNP (density), ShockWave (sonic/acoustic logging), SpectralWave (spectral azimuthal gamma ray), MFRTM (resistivity). The wiper trip without any complications takes approximately 2.5 days on average.
From September to November 2015 experimental operations were carried out at the Verkhnechonskoye field, which included drilling the 178-mm production casing interval in two runs. The first run was performed at the maximum rate till the Central Moti suite. Then the string was pulled out of hole, and the final section was drilled using a BHA with a set of logging tools, but without a spectral azimuthal gamma ray sensor (SAGR), because the rated pressure on the target bottom hole did not allow drilling at the maximum circulation rate. Upon completing the drilling and during the final POOH, standard procedures were carried out and a 178-mm production casing was immediately run into the hole. It should be noted that the operations were performed safely and quickly without any problem. In total, these activities enabled the reduction of the well’s construction time by 12-30 hours depending on the depth of the production casing. After successful pilot operations of double-run drilling, PJSC VCNG decided to conduct an experiment on drilling the interval with Weatherford’s LWD tools in a single run.
To do this, one of the wells at the pad was selected, where the operations were carried out. The casing setting depth was 2,290 m. The well trajectory had neither azimuth turning or a severe dogleg (not more than 2.6°/30 m). Drillability was confirmed by the hydraulic calculations, and the maximum pressure at the end of the interval was 267 atm.
On November 11, 2015 a non-standard BHA was assembled and run in hole for drilling a 215.9-mm interval (Fig. 1).
Experimental drilling operations conducted at the Verkhnechonskoye field
The objective of the operation was to drill an interval to the target depth in one run. As a result, a 1,686.5 m long 585-2,271.5-m interval was drilled with an average penetration rate of 17.3 m/h. The following regime was used for the drilling: the flow rate was 2,100 l/min, the load was 14-17 tons, the pressure drop across the positive displacement motor (PDM) amounted to 25-45 atmospheres. LWD tools were used while drilling, ECD and vibration readings were monitored in real-time. OBM CARBO-DRILL was used as a drilling mud.
The Belsky suite was encountered at the depth of 692 m (true vertical depth of 658.26 m). In the Belsky suite the BHA behaved unpredictably: the zenith angle rose and fell with the intensity of 0.4-1°/30 m, while each stand was reciprocated in the Belsky suite.
The Usolye suite was penetrated at a measured depth (MD) of 1,052 m (true vertical depth – 980.52 m; the calculated dogleg severity of 1-m slide – 0.3-0.38°/30 m). After reaching this suite, the BHA provided the calculated dogleg severity, while the rate of penetration was not limited while drilling. Above the Osa formation a fresh-water pill of 20 m3 was circulated to eliminate the influence of salts of the Usolye suite. The Osa formation was encountered in the interval at 1,460-1,515 m (true vertical depth – 1,337.39-1,380.97 m), where a stabilized section was provided for the installation of an electric submersible pump (ESP).
The Upper Moti suite was penetrated at the depth of 1,548 m (true vertical depth – 1,406.6 m); the calculated dogleg severity of 1-m slide made 0.27-0.34°/30 m, while the pressure surges were observed due to the interbedded formation. In the Upper Moti suite while drilling in dolomites the weight on bit (WOB) was 21 tons (maximum WOB), while the pressure drop across the PDM reached 40 atmospheres.
The Preobrazhen formation: measured depth – 1,886.15 m, true vertical depth – 1,598 m. Each transition zone was underreamed during drilling. A №1 argillite top at the depth of 1,960 m (true vertical depth of 1,619.14 m) was approached with a zenith angle of 75.7°. From this depth to the target the flow rate was reduced down to 1,900 l/min. After passing the argillite zone №1 with rotation, having taken down the top of VCh-1 at the depth of 1,993.6 m (true vertical depth – 1,627.32 m) the zenith angle buildup started with the planned dogleg severity. The argillite zone №2 at the depth of 2,069 m (true vertical depth – 1,641.9 m) was approached with a zenith angle of 81.16°. Further, from the depth of 2,200 m (true vertical depth – 1,659.3 m) VCh-2 top was passed and angle buildup was continued till 90 degrees according to the adjustments of the Customer’s Geology Department. In agreement with the Department, the final 178-mm casing interval target made 2,271.5 m. At the bottom 2 cycles of circulation were made, and wiper trip was also performed in the interval from the bottom hole to the depth of 1,850 m (i.e. 100 m above argillite zone №1) and back without any problems.
After a bottom hole cleanout the BHA was pulled out of hole. The final pulling was accompanied by severe drags amounting up to 10 tons in the interval of 1,521-1,457 m (i.e. in the interval of the Osa formation and the Usolye suite), where a fresh-water pill had not been pumped. When the BHA was inspected, it was found that the axial play on the PDM was 5 mm, and our company’s equipment had no signs of wear. Drilling was successfully completed on November 18; the BHA was pulled out of hole and dismantled the next day.
Conclusions
1) The 178-mm casing interval has been drilled in one run at a good penetration rate equal to 17.3 m/h, which represented the average number for the Customer.
2) While drilling with rotation till the Central Moti suite the pressure drop amounted to 45 atm, then to 40-30 atm. The low pressure drop may be associated with the interbedded rocks, limited flow rates, as well as bit wear.
3) The PDM with an oil-resistant elastomer has lasted for the warranty non-failure operating time (147.1 hours of circulation); the inspection showed an axial play of 5 mm (permissible value).
4) The calculated dogleg severity of the BHA used in the project is similar to that of a BHA without an LWD suite (the percentage ratio of the rotor/slide is identical, and the comparison was based on similar interval profiles).
5) Despite a large number of stabilizers in the BHA (2 additional full-sized components), the torque and weight corresponded to the calculated values.
6) 178-mm casing was run in hole without complications.
Drilling schedule of the first well
The production casing interval in the first well was also drilled in one run. Then wiper trip was performed together with logging tools. As shown in the drilling schedule (the production casing depth is similar to the second well), it took 5.5 days to drill the interval (the schedule plan provided for 6.5 days), while the operations following the drilling of the production casing interval were supposed to take 4.5 days, and the actual time amounted to 5 days.
Drilling schedule of the second well
In the second well it took 6 days to drill the production casing interval (the plan provided for 7 days), and the actual time for operations following the final drilling made 4 days (compared to 3.5 days planned). This included complicated pulling out of hole with reciprocation, which took additional 16 hours; there were problems while wiper drifting of the casing with a BHA with a riber, which required 3 hours of additional time. Thus, the duration compared to the first well took about 2 days, other factors being equal. This corresponds to the actual time spent on the wiper trip with logging tools in the first well, which makes a little less than two days.
Results of using a BHA with Weatherford LWD tools
Technology:
• Suitable arrangement of BHA components (lengths) both for assembly on the drilling site and for drilling.
• Source loading and programming were carried out without problems. IDS sensor (10-11 m from the drill bit) allows taking measurement and accurately estimating and predicting the official measurement from HEL (38-39 m from the drill bit) to be received after another stand drilled, which means reducing the non-measured zone (it is usually 17 m).
• A large number of centering components with a simple well profile (no azimuth turning) does not affect the drilling process and drill pipe movement, i.e. the arrangement of BHA components is generally satisfactory. However, assembly, programming and loading takes approx. 5 hours, which corresponds to the time specified in the technical part of the contract with the Customer.
Time:
• Drilling in one run using LWD tools saves approx. 2 days in the well’s construction.
• The penetrated argillite zone remains open for a much shorter time period (almost 2 days), which reduces the risk of collapse.
Geology:
• The Customer’s Geological Department received information in real time allowing them to better understand the vertical of the production casing RIH, to get the profile data processed and analyzed by Weatherford’s petrophysicists in a few hours after POOH.
• As proven by the experience, when drilling the final section with a similar BHA to other wells, the significant length and rigidity of the BHA prevents its use when using an azimuth turn by more than 60 degrees. When the casing setting depth exceeds 2,700 m (even without azimuth turning), it is a problem to deliver weight in the lower intervals while slide drilling, which significantly reduces the rate of penetration, and when the drilling rate exceeds 60 m/h, log recording quality may become poor.
Upon the completion of the operations, it may be said that the use of a BHA with LWD tools to drill the production casing interval directly from under the surface casing significantly saves well construction time – by almost 2 days. Additionally, the risk of well collapse is mitigated, and geological specialists can promptly receive accurate information about the profile of the well. However, the selection of such a BHA to drill the entire interval requires an individual approach to each well and the consideration of all possible risks, including sticking; and it is also necessary to take into account the specific features of the well profile, which is important for hydraulic calculations and calculations of the complete load transfer.
At the moment, several candidate wells have already been selected for further testing. The implementation of this practice on a regular basis will accelerate the delivery of new wells into operation at the Verkhnechonskoye field. Specialists of the VCNG Drilling Department jointly with Weatherford experts are constantly trying to find ways to reduce well construction times and mitigate drilling risks.
Andrey Klabukov, Project Coordinator, Weatherford Russia
Andrey Dubrovin, Regional Operation Manager, Drilling Services, Weatherford Russia
Vladimir Shulga, Director of Drilling Department, PJSC VCNG
