Well Planning Objective

the plan must be altered during the course of drilling the well when unforeseen drilling problems endanger the crew. Failure to stress crew safety has resulted in loss of life and burned or permanently crippled individuals.

The second priority involves the safety of the well. The well plan must be designed to minimize the risk of blowouts and other factors that could create problems. This design requirement must be adhered to vigorously in all aspects of the plan. Example I.I illustrates a case in which this consideration was neglected in the earliest phase of well planning, which is data collection.

Example 1.1

A turnkey drilling contractor began drilling a 9.000-ft well in September 1979. The well was in a high-activity area where 52 wells had been drilled previously in a township (approximately 36 sq mi). The contractor was reputable and had a successful history.

The drilling superintendent called a bit company and obtained records on two wells in the section where the prospect well was to be drilled. Although the records were approximately 15 years old, it appeared that the formation pressures would be normal to a depth of 9,800 ft. Since the prospect well was to be drilled to 9,000 ft, pressure problems were not anticipated. The contractor elected to set 10%-in. casing to 1,800 ft and use a 9.5-lb/gal mud to 9,000 ft in a 97/s-in. hole. At that point, responsibility would be turned over to the oil company.

Drilling was uneventful until a depth of 8,750 ft was reached. At that point, a severe kick was taken. An underground blowout occurred that soon erupted into a surface blowout. The rig was destroyed and natural resources were lost until the well was killed three weeks later.

A drilling consultant retained by a major European insurance group conducted a study that yielded the following results:

1, All wells in the area appeared to be normal pressured until 9,800 ft.

2, However, 4 of the 52 wells in the specific township and range had blown out in the past five years. It appeared that the blowouts came from the same zone as the well in question.

  1. A total of 16 of the remaining 48 wells had taken kicks or severe gas cutting from the same zone,
  2. All problems appeared to occur after a severe 1973 blowout taken from a 12,200-ft abnormal pressure zone.

Conclusions

  1. The drilling contractor did not research thoroughly the surrounding wells in an effort to detect problems that could endanger his well or crews.
  2. The final settlement by the insurance company was over $16 million. The incident probably would not have occurred if the contractor had spent $800 to obtain proper drilling data as the drilling consultant had done.

Minimum Cost. A valid objective of the well planning process is to minimize the cost of the well without jeopardizing the safety aspects. In most cases, costs can be reduced to a certain level as additional effort is given to the planning (Fig. 1—1). It is not noble to build "steel monuments" in the name of safety if the additional expense is not required. On the other hand, monies should be spent as necessary to develop a safe system.

Usable Holes. Drilling a hole to the target depth is not completely satisfactory if the final well configuration is not usable. In this case, the term "usable" implies the following:

  • The hole diameter is sufficiently large so an adequate completion can be made,
  • The hole or producing formation is not irreparably damaged.
Oil Well Planner

Well planning effort

Fig. 1-1 Well costs can be reduced dramatically if proper well planning is implemented

This requirement of the well planning process can be difficult to achieve in abnormal pressure, deep zones that can cause hole geometry or mud problems.

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