This paper presents a case history on drilling of an ultra-deep exploratory well with a lot of problems and final solution in a complicated K structure in Uzbekistan. Drilling troubles include serious stuckpipe resulted from drilling-in the unexpected high pressure brine formation, malfunction of the high density drilling fluid system, and subsequent failure of the fishing jobs, unsuccessful sidetracking, bad job of cementing, etc.After the drilling fluid system was improved, the high pressure layers were isolated, and the proper drilling measures were carried out, the second sidetracking gained success and the well was completed. Afterwards, an adjacent ultra-deep well in the same structure was smoothly drilled and completed by means of optimization of the casing programs, drilling fluid system and technical measures.Drilling practices of previous offset well indicated that the formation is pay zone and produced oil, while the same formation at the same depth in the well JD3# produces brine water, which resulted in overflow during twice sidetracking of the same formation. The high and low pressure layers existed in the same section after drilling-in brine formation would produce complex against drilling and subsequent operations, therefore a 7-inch liner was set to isolate the high pressure formation, so as to create a good condition for deeper drilling operation. High-density drilling fluid with good precipitation stability and lubricant anti-sloughing properties also contributed to the success in drilling of high pressure brine layer and salt gypsum formation.Accurate determination of the must-be-blocked point is the key to the success. Drilling of the well with problems and its final solution could be used for a technical reference as drilling in deep or ultra-deep wells in similar geologically complicated oil and gas fields.

ChuanDongBei Field of Sichuan Basin is a HPHT deep gas reservoir with multiple pressure systems, with maximum formation temperature up to 156 oC and pressure gradient of 1.86 at the depth of 6500m. Part of the well section contains more than 5% CO2 and near to 10% H2S, so drilling operation is extremely challenged. Firstly, this paper introduces drilling challenges such as lost circulation, severe caving-in, pipe sticking in upper section, sour gas corrosion problems, low penetration rate in the middle and deep section. Secondly, a lot of available key drilling technologies are innovated and provided, including casing program optimization, air and nitrogen drilling to improve ROP, combination drilling with anti-HT motor and fit for purpose PDC bits, anti-HT mud along with losses prevention technologies such as MPD, anti-gas channeling and big temperature difference cementing slurry in the long interval, BOP and H2S sour gas monitoring system with emergency plan and some management advices for deep HTHP containing sour gas wells. Finally, some unexpectable application results regarding these techniques to solve a series of drilling difficulties have been mentioned according to 40 wells cases. Take well LG01-XY as an example, which was improved average ROP to 6.4m/h, extended the footage to 1713m in one specialized bit with air hammer, reduced drilling period to 145days, reached “zero pollution, zero harm, zero accident” achievement during H2S interval, got premium cementing result and well bore qualify. So it could be used as a technical reference while drilling in deep HTHP containing sour gas wells in similar geologically complicated gas fields.

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe wells in the Kenkiak Under-Saltdome (KUS) oilfield in Kazakhstan are difficult to drill and complete due to the complicated geological conditions. Historically, among 42 wells which had been drilled in this area 40 wells were abandoned; only 2 wells are in production. The wells were completed by casing perforation, with low averaged daily rate of production 64 tons per well. After 1997, initially, wells were continuously completed by casing perforation, with averaged daily rate of production around 100 tons per well.

It was difficult to drill and complete the wells in the Kenkiak Under-Saltdome oilfield in Kazakhstan due to complicated geological conditions. Among 42 wells which had been drilled by former operator 40 wells were abandoned; amid 40 abandoned wells 12 were engineering abandoned; only 2 wells were capable of production with 38 to 69 tons of oil per day. Because of low drilling rate of success, long cycle of drilling, and low production, the former operator regarded the field an unable to be developed one. Consequently the field had not been put into production since its discovery 30 years ago. In order to increase the productivity, near balance drilling and open hole completion have been accepted for vertical wells in the beginning in high pressure low permeability fractured carbonate reservoir. The first trial met with success and initial day rate of production was as high as up to 480 tons of oil. Subsequently, near balance drilling and open hole completion have been adopted for other vertical and high-angle wells, average day rate of production exceeds 300 tons per well. However, a few wells completed open hole encountered tubing blocked when put into production, which resulted in those wells off production. To prevent the wells from tubing blocked during putting into production, as well as to maintain high productivity, subsequent wells that are not suitable for open hole completion have been liner completed. Average day rate of production of those wells completed with liners also exceeds 300 tons per well. Production of some wells completed open hole or liner exceeds 1000 tons per day per well. Open hole completion and liner completion have greatly increased productivity as compared to those wells completed perforation, turning it from an unable to be developed marginal field into one with annul capacity of 2 million tons of oil. Background The Kenkiak Under-Saltdome (KUS) oilfield was discovered by former USSR in 1971. The geology of the field was so complicated that the drilling and completion were hard to be accomplished. The complicated geological conditions could be reflected in, but are not limited to, the following aspects:The salt, gypsum and interbeded plastic mudstone in the Permian were subject to swelling and creeping thus resulting in stuck pipe and crush casing.Gas cut from the shallow-layer hi-pressure gas formation lain in the salt dome could lead to blowing out.The lower Permian and the Carboniferous, belonging to hi-pressure reservoirs, with active oil and gas, near formation pressure and lost-circulation pressure, and narrow gap of safe density of drilling fluid, were subject to lost circulation and blowing out at the same time, or stuck pipe resulted from wall collapse.The extremely thick mudstone layer interbeded with glutenite and hard mudstone in the non-saltdome upper Permian series could exert a great impact on safe and quick drilling in. The average well depth of the Permian reservoir is 4183m, while the average drilling cycle is 24.62 rig-months; the average well depth of the Carboniferous reservoir is 4543m, while the average drilling cycle is 33.73 rig-months. Frequently occurred complex and accidents, low rate of penetration and high cost of drilling, especially engineering abandoned 12 wells impeded the achievement of deep targets and severely restricted the exploration and development of the KUS reservoir. Introduction An investigation revealed that out of 36 wells drilled by former operator in oil zones of the KUS reservoir, 26 wells (accounting for 72.2%) encountered oil and gas invasion and blowout; 13 wells (36.1%) circulation loss; 13 wells (36.1%) wall collapse, hole shrinkage and stuck pipe. 28 wells in total incurred the above complicated conditions, accounting for 77.8%. A weighted drilling fluid was used to balance the high formation pressure, over balance drilling (OBD) was utilized.