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