By Frank Hartley • Houston
Conveyed without a wireline
A second, open-hole logging operation has been completed in the Saltfleetby gas field, UK, using a wireless, open-hole Compact Memory Logging (CML) system provided by Reeves Oilfield Services.
Saltfleetby is the UK’s largest gas field, with initial in-place reserves of 119 bcf, and with production exceeding that of many North Sea fields. Saltfleetby is operated by Australian independent Roc Oil.
The CML was deployed successfully in the horizontal Saltfleetby-5 well in September 2001 following earlier CML operations in Roc’s Keddington 2z well. This was the first use of CML at a UK location, and was followed in December 2001 by another successful horizontal operation in Saltfleetby-6y. A quad-combo measurement string (density – neutron porosity, gamma ray, array induction, and sonic velocity) was conveyed without a wireline on drill pipe in CML Memory Pipe Conveyed Logging mode (Memory PCL).
Memory PCL does not use the wireline, wet-connect system needed in conventional wireline PCL, so logging tools are run in the well more quickly. In Saltfleetby-6y, for example, the time between rig-up and rig-down was less than 18 hours, compared with an estimated 28 hours for a wireline PCL operation. Safety is also improved because drilling mud can be circulated during the operation to control the well.
Saltfleetby-6y was completed in January, confirming gas reserves in the previously untested southern area of the field. The well also intersected a gas-water contact, confirming it to be 19 m deeper than had previously been assumed for reserves calculations. Information gathered in Saltfleetby-6y has contributed to increased estimates of likely recoverable reserves from the field, up by 13.4 bcf, which is more than the 2001 production of 12.1 bcf. The well was successfully put on production on Jan. 20, 2002.
The tools were developed to improve operational efficiency and well access across a broad range of well types. They have been used in over 7,000 logging operations in North America, Australia, and Europe since 1998, over 100 of which have been with the recently introduced CML system.
Traditional approaches to hole-cleaning problems in high angle wells include high viscosity sweeps, increased rotary speeds, fast pump rates, frequent short trips, and/or lubricants. These methods may buy time if the well reaches total depth quickly. However, when there is considerable hole to make, hole cleaning must be effective or the operator may face sidetracking the well. Therefore, the focus is shifting from the old "cuttings removal" models to the application of a sweep method that actually removes the accumulated silt bed from the low side of the hole.
Excellent results are being achieved in the Gulf of Mexico using a fully circulated weighted sweep (3-4 ppg over drilling mud weight; 200 to 400-ft column in the annulus). The weighted sweep is built from the drilling mud in use and the yield point remains at its acceptable drilling value. Any increase in viscosity is minimal.
Recent case histories show that if a weighted sweep is pumped at regular intervals at the normal circulating rate, while rotating pipe at 60 rpm once the sweep reaches the bit, and allowed to return to surface, it carries a significant and visible quantity of silt to the shakers. Operators who now routinely use this method have been convinced by radically different before-and-after hole conditions on complex, high angle wells.
SCSSV for deep, HP/HT reservoirs
Many of the remaining major opportunities for new hydrocarbon development include reservoirs that are deep and/or have high pressure/high temperatures (HP/HT). Such reservoirs present challenges not only during the drilling and evaluation stages of development, but for completion plans and future intervention activities, as well. In challenging, hostile environments, an effective completion is critical to long-term well perfor- mance.
In deep and ultradeep reservoirs, completion devices and equipment must withstand conditions associated with extreme depths, including HP/HT. Offshore, deep well completions also must operate reliably under the severe conditions inherent to the deepwater environment. Completion activities at the sandface require considerable design, analysis, and teamwork between the operator and service company for selecting the appropriate fluids to avoid formation damage and choosing a suitable well completion to avoid long-term sand production. The completion also must ensure a reservoir’s efficient recovery, maximizing hydrocarbon production while controlling unwanted fluids. Additionally, subsurface well control is required to prevent uncontrolled well flow and shut in the well in the event of a disaster.
Each offshore hydrocarbon province around the world presents its unique challenges that must be met by safety equipment. Safety equipment and systems are required to perform reliably in severe service conditions and often under stringent governmental regulations. Moreover, they often must withstand harsh operational requirements, for example extreme depths. In fact, the world record setting depth for a surface-controlled subsurface safety valve (SCSSV) was recently extended successfully without incident.
(Left)Field-proven designs and record-setting field applications have resulted in the TRC-DH safety valve system's use in 75% of all wells in 1,000 ft or more water depth
Schlumberger installed a 4 1/2-in. TRC-DH safety valve at a depth of 9,801 ft in the first well of Marathon Oil Company’s Camden Hill Project, part of the Canyon Express Field Development Project, situated in 7,200-ft water depth. To achieve this feat on time took an aggressive manufacturing schedule and operator/service provider teamwork. The reservoir pressure was 7,400 psi, while the shut-in pressure at the 10,000-psi rated SCSSV was 6,500 psi. Minimum and maximum temperatures at the valve setting depth were 75 and 150°F, respectively, with the bottomhole temperature at the perforations being 155°F. The depth to the top of the well’s upper perforations is 13,855 ft. The previous world record was achieved six years ago in Shell’s Mensa subsea development, where a TRC-DH safety valve was set at a depth of 8,934 ft in a well drilled in 5,300-ft water depth.
Designed for deepset and subsea applications, the TRC-DH series safety valves have performed effectively at depths where other safety systems proved ineffective. The safety valve’s redundant hydraulic operating systems have a balancing mechanism so that they are tubing pressure insensitive. In other words, the effect of tubing pressure on the valve’s hydraulic operating piston is negated. This reduces the pressure rating required for the hydraulic control system through the wellhead and the emergency shut down system at surface.
Testing has proven that these valves can be run at depths beyond 10,000 ft, enabling their positioning below the hydrate or paraffin deposit regions to increase operating efficiency. With two separate and complete operating piston systems connected by individual control lines, they have complete operating redundancy for extended valve life, which is critical for deep applications where intervention costs can be prohibitive. Additionally, filtered control fluid improves the valve’s life cycle. This SCSSV series also has a HP/HT version.
In addition, two other types of safety valves have been designed specifically for HP/HT applications. The Pinnacle safety valve series are non-elastomeric flapper-type valves that are reliable, cost-effective, and can operate in sweet to severely corrosive environments with working pressures and temperatures to 15,000 psi and 400°F, respectively. Also proven in HP/HT, severe-environment field applications, the TRDP/TRSP series safety valves have dual or single-piston configurations with all-metal seals, built for withstanding pressures to 20,000-psi and temperatures to 400°F. Both HP/HT valve types are designed to have long service lives at such extreme pressures and temperatures.