Abstract

Since the turn of the millennium, non-retrievable drilling with casing technology has been introduced to the Asia Pacific region. Soft formations encountered in offshore drilling environments have promoted the successful application of casing drilling technology for conductor and surface casing installation1,2,3.

The Weatherford system employs a simple aluminium based casing drill shoe and float collar assembly, driven by a surface drive system that transmit torque from the top drive to the casing string4. Upon reaching targeted casing shoe depth, the cementing operation can commence almost immediately. The next conventional drilling assembly can then drill out the casing drilling assembly using a traditional PDC or rock bit without requirement for a special drill-out bit.

The Maari Development Project in New Zealand is situated in an ideal soft drilling environment that is within the capability of the drillable drill shoe. During the project planning stage, non-retrievable drilling with casing technology was highlighted as a viable technology to improve drilling efficiency, reduce cementing times, protect the weak shallow formations the platform foundation depends on, and reduce potential risks. Substantial engineering effort and time have been invested to tackle all relevant technical issues.

This paper presents the Maari Project's 24" conductor drilling programme, covering the entire process from the planning stage through to the execution, which resulted in successfully installing and cementing nine strings of 24" conductor ahead of the time allocated to conventionally drill, case, and cement eight strings.

Background

The Maari oil field in permit area PMP 38160 was discovered in 1983. Through various acquisitions PMP 38160 is now operated by OMV New Zealand Limited (69%) on behalf of its joint venture partners Todd Maari Limited (16%), Horizon Oil International Limited (10%), and Cue Taranaki Pty Ltd (5%). The permit contains the Maari discovery and is located close to another oil discovery the Manaia field in block PEP 38413.

Five production and three injector wells were planned for the initial development. In addition, provision was made for the construction of a further 4 wells at a later stage in Project life. All these wells can be drilled from or tied back to the wellhead platform (WHP) "Tiro Tiro Moana", which is equipped with 12 drilling slots. The waxy nature of the crude requires heating downhole, on the wellhead platform as well as the FPSO "Raroa" to successfully transport the crude.

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