In 2012, Pemex announced some major oil discoveries in a new exploration region with its first two Ultra Deep Water exploration wells. The first achieved the deepest well ever drilled in Mexico to a depth of 6,119 m and the second achieved drilling in the deepest water depth at 2,900 m. These wells have confirmed that Perdido has a high potential for commercial production. This reservoir was found in Lower Tertiary geological system.
Problems incurred while drilling out from under the large casing sizes (22”, 18”, 16”) with tandem hole enlargement bottom hole assemblies. Shallow reservoirs need to be evaluated for hydrocarbon potential, but these shallow hole sections are in very large hole sizes that require optimizing the drilling and formation evaluation. The objective here is to drill, evaluate and enlarge with the same BHA. During the same trip, the simultaneous enlargement of the hole is made to avoid a second under reaming trip (22”, 20”, 17 ½”, 16 ½”, 13 ½”).
The shallow vertical depth of the reservoirs and the shallow geohazards requires a directional well design avoids the shallow hazards and the directional build section is intended to intersect the drilling target. An alternative strategy is to acquire the full suite of wireline logs in a dedicated 12 ¼” pilot hole. Subsequently, an under-reaming trip is made for the hole enlargement. This second option is also very time consuming.
The drilling group has evolved a tandem drilling assembly from traditional hole enlargements of 17½”x20" or 12¼”x 14 3/4" to more complex simultaneous drilling and hole enlargements BHA’s of 12 ¼”x 16 ½”x20” or 12 ¼”x14½”x17 ½”. These new assemblies incorporate the rotary steerable system with mechanical and hydraulic hole openers, plus a complete set of LWD measurements for supporting the real time formation and geo-mechanical evaluation. This combination assures that in one run, the hole is drilled, evaluated, and enlarged, reducing well bore stability risk, and saves time and resources.
Significance of Subject Matter
Pemex evaluated the reservoirs in the discovery of commercial quantities of hydrocarbons that can possibly double the oil reserves of Mexico
Vallejo, Victor Gerardo (Pemex E&P) | Olivares, Aciel (Pemex) | Crespo Hdez, Pablo (Pemex E&P) | Roman, Eduardo R. (Pemex E&P) | Maia, Claudio Rogerio Tigre (Halliburton) | Guajardo, Michael (Halliburton)
A well testing operation was performed to confirm productivity potential in an ultra-deepwater area where a 5660-ft exploratory well had been drilled. This was a gas well, drilled from a semi-submersible drilling rig. As well testing from submersible rigs is a critical and sensitive operation; all planning had been carefully reviewed by the operator to ensure a safe, environmentally friendly operation.
The formation of hydrate plugs during ultra deepwater well testing is a critical concern, since water can be trapped and form a solid crystalline structure around gas when there are low temperatures near the mud line. This hydrate formation is a common occurrence in deepwater drilling operations, particularly while using water-based mud. Thermo-dynamic inhibition may not be effective in these cases, as several limitations in achieving the required injection rate exist.
Oilwell testing operations in deep and ultra-deep water have become common practice around the world, and vast experience with these types of operations has been acquired; experience with gas wells, however, has not been as comprehensive, and only a few gas wells have been tested under the conditions presented in this type of scenario. Because of the low number of gas wells tested in these deepwater conditions, best practice information is limited.
The intention of this paper is to present a case history and the lessons learned during a well testing operation in which water production in the gas-well was greater than anticipated during the clean-up period. A massive hydrate plug was formed while coiled tubing was being pulled out of hole, and the coiled tubing became stuck. The steps taken to free the coiled tubing will be discussed, and the discussion will include:
• Conditions that must be present to form hydrates
• How the problem in this case was resolved
• How to help prevent hydrate formation
• Best practices for well testing in deep-water gas wells to maintain safety and economic viability.
This case history discusses a gas well being drilled with a semi-submersible drilling rig in ultra deep water, offshore Mexico.