Use of a New Four-Component Drilling System in the Attaka Field
- N. Sawolo (Unocal Indonesia Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling Engineering
- Publication Date
- December 1989
- Document Type
- Journal Paper
- 321 - 328
- 1989. Society of Petroleum Engineers
- 5.3.4 Integration of geomechanics in models, 1.11 Drilling Fluids and Materials, 1.6 Drilling Operations, 1.5.1 Bit Design, 1.9.4 Survey Tools, 1.6.6 Directional Drilling, 1.12.1 Measurement While Drilling, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.6.1 Drilling Operation Management, 4.5.5 Installation Equipment and Techniques, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.5 Drill Bits
- 0 in the last 30 days
- 114 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 5.00|
|SPE Non-Member Price:||USD 35.00|
Unocal Indonesia Ltd. significantly reduced drilling time and cost by introducing a four-component drilling system in the Attaka field. The new drilling system includes use of polycrystalline-diamond-compact (PDC) bits, a low-toxicity oil-based mud (LTOBM), a measurement-while-drilling (MWD) survey tool, and a steerable positive-displacement mud motor. This paper presents a case study that shows the advantages of the new drilling system over the conventional drilling technique.
The Attaka field, offshore East Kalimantan, Indonesia, was developed by Unocal Ltd. and Indonesia Petroleum Ltd. under a production sharing agreement with Pertamina, the Indonesian state-owned oil company. Field development began after its discovery in 1970. Most wells were drilled to 7,500 ft [2286 m] vertical depth with conventional KCl/polymer muds and rock bits.
In 1984, a new development drilling phase began in the Attaka field. In addition to penetrating reservoirs present in existing wells, we explored deeper objectives. We also introduced our four-component drilling system, which led to significant improvements over conventional drilling methods (e.g., wellbore instability problems ended, bit life and penetration rates increased, and drilling time and cost decreased).
Drilling System Components
LTOBM. The first component of the new drilling system, LTOBM, was a major factor in the success of the system because it successfully eliminated borehole instability problems.
The absence of hole instability when oil-based mud is used has long been realized, but the toxicity of conventional diesel-based drilling fluid precluded the use of oil-based mud in many offshore installations. Development of oil-based mud since the mid-1970's, however, has greatly reduced its toxicity, and it is now used offshore.
In the Attaka field, the absence of hole instability when LTOBM was used directly contributed to a reduction in drilling time. An even more impressive performance was achieved when the LTOBM was combined with the rest of the system.
Table 1 summarizes properties of a typical LTOBM used in the Attaka field.
PDC Bit. The second component on the Attaka drilling system is the PDC bit. The fundamental difference between PDC and rock bits is in the ways the bits drill the formation. A PDC bit relies on the scraping action of the thin layer of polycrystalline diamond on its cutters; a rock bit depends more on the gouging action of its teeth. Both PDC and rock bits were run in the first few wells of the new development drilling phase. Results from these runs indicated the potential increases in penetration rates and the longer bit lives of PDC bits. During this early phase, many different types of PDC bits were tried with varying success. On the basis of the results of the runs, we decided either to eliminate the bits or to develop them further to obtain better drilling performances. As a result, 12 1/4-in. [31-cm] -bit runs in excess of 3,000 ft [915 m] were expected, and one run close to 7,000 ft [2135 m] was achieved. For the 8 1/2-in. [22-cm] bit, the record is more than 11,000 ft [3350 m] on three runs. The evolution, experiments, and design modifications of PDC-bit use in the Attaka field are discussed later.
MWD Survey Methods. The MWD tool, which was run on all Attaka directional wells, is a downhole survey sensor that transmits information to the surface by generating a series of pressure pulses in the mud column that are picked up and decoded in the surface package to give wellbore directional data.
One advantage of the MWD tool is that it continually monitors and updates information on the tool face of the bent housing of the mud motor. Greater directional control is possible because more surveys are obtainable. This reduces drilling time because the well course is followed more faithfully, which correction runs. The elimination of lengthy and sometimes risky wireline surveys further decreases drilling time.
Downhole-Steerable Positive-Displacement Mud Motor. The combination of LTOBM, PDC bit, and MWD tool resulted in more drilling footage. To realize the advantages of this combination fully, trips for bottomhole assembly (BHA) changes must be minimized. With the introduction of the downhole-steerable positive-displacement mud motor, trips for BHA changes were minimized and sometimes eliminated because of its steering capability. The full advantage of longer PDC bit life could therefore be exploited.
We used a steerable mud motor with a built-in bend in its double-tilted universal (DTU) joint housing. This DTU creates a bit offset, which gives the motor its steering capability. Changes in wellbore inclination and azimuth are achieved by aligning this bend to the required orientation and drilling off the section with no drillstring rotation-i.e., "steering." Once the required inclination and azimuth are achieved, drillstring rotation is resumed for the straight-hole section.
Table 2 gives the specifics for a typical motor for a 12 1/4-in. [31-cm] hole.
|File Size||1 MB||Number of Pages||8|