Jun Jia

Drilling Fluids and Solids Control Technology

Core drilling, expanding drilling (reaming) and non-core drilling were the main drilling methods employed for CCSD-1 Well. Different drilling methods needed drilling fluids with different performances to ensure implementation of the drilling technologies. Roller bit was employed for expanding drilling and non-core drilling with bigger debris granule (2–5 mm) produced while diamond bit was employed for core drilling with very fine debris (5–100 μm) produced. Rotary table drive with low rotation speed of 30–60 r/min was employed for non-core drilling and expanding drilling while downhole PDM and hydro-hammer with high rotation speed of 160–200 r/min were employed for core drilling. The pump capacity of drilling fluid was 25–35 L per second for non-core drilling and 9–11 L per second for core drilling. So, discrepancy was a little wide for the performance requirements of drilling fluid to different kinds of drilling methods. Carrying capability of mud was required to be good to clean away bigger debris granule produced in non-core drilling and expanding drilling, and then improve drilling efficiency finally, while core drilling required mud with the performance of not only be good at carrying, but also suspending debris while circulation was stopped, what’s more, the requirement of driving medium as a bottom power system should be satisfied. Simple for preparation, easy regulation of performance and convenient management were all required for drilling fluid in consideration of field preparation and management. For saving cost and reducing discharge, it was best to use a single drilling fluid system at drilling field, thus when drilling technology changed, the requirement of the changed drilling technology could be satisfied without changing drilling fluid system but with only simple regulation of its performance. The LBM-SD drilling fluid system specially designed for CCSD-1 Well was employed to accomplish core drilling, expanding drilling and non-core drilling.

Drilling Engineering Design

As a huge systems engineering project, China Continental Scientific Drilling (CCSD) engineering project consisted of five main sub-projects and one subsidiary sub-project. The five main sub-projects included drilling sub-project, borehole geology and analysis and test sub-project, borehole logging sub-project, geophysics sub-project and information sub-project; while the subsidiary sub-project denoted civil engineering. Among these sub-projects, drilling sub-project was the key, which was the precondition of conducting other sub-projects. Only by obtaining core, rock samples, gas and fluid samples through drilling project could analysis and test sub-project be started and only after borehole completed that a passageway could be available for logging and for geophysical tests, so as to obtain the underground material information. Besides, drilling sub-project was the one which cost the largest investment and the longest time, and with extreme difficulty. Therefore the successful completion of drilling sub-project determined the success of the whole scientific drilling engineering project.

Drilling Data Acquisition

What CCSD-1 Well encountered were not only the deep hole to be drilled but also the complex formations to be met, and then a wide variety of drilling technologies were adopted during the difficult constructions. In order to improve drilling efficiency and reduce drilling accident, drilling process monitoring must be strengthened, so as to improve the levels of on-site monitoring, decision-making at drill site and drilling data processing. So a complete set of drilling data acquisition and processing system was indispensable for deep well drilling, which could assist to identify the bottom-hole conditions, improve the level of drilling decision-making, and reduce accidents and construction costs. At the same time, the drilling data acquisition system was also an important data source for drilling management.

Reaming Drilling Techniques of Hard Crystalline Rock

The main problems encountered in the reaming drilling of CCSD-1 Well were as follows: (1) Hard formation was difficult for drilling: according to the cores recovered from the pilot hole drilling, the formation encountered by reaming drilling was crystalline rock (mainly eclogite and gneiss), with drillability grades of 8–9 in most cases, the major was grade 9, and the drillability of a few rocks was even up to grade 10–11, and the penetration rate per hour was lower.

Well-Deviation Control Techniques for Strong Dipping Strata

The factors influencing hole deviation are extensive, they are generally divided into three kinds, the geological factor, the technical method factor and operation factor. The geological factor mainly includes the rock structures, anisotropy, the schistosity and bedding, soft and hard interbeds and occurrence and so on. The technical method factor mainly includes the deflection in hole opening, the well wall annular space, the rigidity of the bottom drilling tool assembly and deflection state and so on. The operation factor mainly is the feeding WOB. During drilling CCSD-1 Well, the strata factor and features of bottom drilling tool assembly were the important factors. Since the strata factor was unchangeable, so the reasonable bottom drilling tool assembly was mainly taken with help of the WOB control technique to prevent the hole deviation.

Casing and Well Cementation

The casing program of CCSD-1 Well was different from that of conventional oil drilling and water well drilling in two aspects: not only were the standards of casing program different but also the moving casing techniques employed. In oil drilling, a casing program of 508.0 mm (20 in.) × 339.7 mm (133/8 in.) × 244.5 mm (95/8 in.) × 177.8 mm (7 in.) was generally employed, whereas in CCSD-1 Well a casing program of 339.7 mm (133/8 in.) × 273.0 mm (103/4 in) × 193.7 mm (75/8 in.) × 127.0 mm (5 in.) was adopted in design and in construction.

Hard Rock Deep Well Core Drilling Techniques

It is well known that core is the most important carrier of deep underground geological information, either for conventional geological drilling and oil and gas drilling, or for scientific drilling which serves for earth sciences. Therefore, how to obtain high quality core under the different conditions is an eternal problem that always lies ahead of drilling engineers. Core drilling techniques are the main key techniques for CCSD-1 Well, directly affecting the success of the whole project, and its efficiency and quality.

Technical Economical Analysis

CCSD-1 Well was officially started on June 25th, 2001, and the designed coring drilling tasks was completed on January 23rd, 2005, when drilled to 5118.2 m. From January 25th, 2005 to March 8th, drilling tools were tested and the well was drilled to 5158 m, and the whole well drilling constructions were completed.

Well Site and Drilling Equipment

CCSD-1 Well is located at the southwest of Donghai County, Lianyungang City, Jiangsu Province, and 18 km (Fig. 3.1) from Donghai County. There is a south-north village byway on the west side of 100 m from the well site, and a village highway (Fengquan Road) on the east side of 300 m from the well site. About 2 km along the road to the south is Maobei Village; about 3 km along the road to the north is just jointed with Xuzhou-Lianyungang Highway, from which is about 15 km to Donghai County. Shihu Village Railway Station of East Longhai Railway Line is 8 km away on the north side of the well site, and Lianyungang Port and Airport (Baitabu) are respectively 86 and 32 km away on the east side of the well site.

Diamond Core Drill Bit

Being an important part of core drilling techniques, diamond core drill bit is a basic prerequisite to improve drilling efficiency and core recovery, and its application results (drilling rate and service life) play an important role to influence the economy and the technical indexes of drilling construction.