Geosteering: Part I – Introduction

What is geosteering?

Geosteering is the esoteric art of squiggly-line matching.  Ok, that may be an unfair summary, but for US-onshore horizontal wells, geosteering is the essence of proper well positioning.

Really, what is it?

For US-onshore horizontal wells, geosteering is the real-time correlation of real-time drilling data against offset well data.  Geosteering is done in “real-time” (as soon as data are made available) with “real-time” data (acquired and distribute as the well is drilling) in order to pilot the active well along its “intended” path.

Life-cycle management

Geosteering operations during the active well’s drilling life-cycle should at least include:

  • Checking that all offset well data are correct and properly loaded
  • Checking that all active well data are correct and properly loaded
  • Reviewing the drilling plan: casing points, kick-off point, landing point, lateral path, drilling variables (pressures, mud weights, etc) and any special instructions
  • Matching marker beds as the well approaches its kick-off point (KOP)
  • Adjusting the landing point as the curve is built
  • Adjusting the lateral drilling-targets as the lateral is drilled
  • Auditing (re-correlating) data against newly acquired offset well data
  • Adjusting future well position plans to match circumstances encountered during drilling operations

And of course, clear and effective communication with all interested parties (drilling engineers, company men, directional drillers, etc) should be present at all stages.

Good intentions pave the road to corrections

Well position plans are developed to maintain maximal reservoir contact within the realm of both available drilling technology and achievable drilling costs.  There are several wrenches that can be thrown into these plans, such as, but not limited to:

  • Poor seismic resolution
  • Thickening and thinning of the reservoir
  • Structural changes
    • Folding
    • Faulting
    • Steeper or subtler dip changes
  • Unexpected drilling parameters

Plan of attack

Geosteering goals, as they relate to the drilling team, will vary based on each drilling team’s business needs, which may include:

  • Maximal reservoir-target contact
  • Drilling efficiency with a contingency for the unexpected
  • Balancing between drilling the sweetspot and drilling on budget

Not all team goals will be represented in the above list.

NEXT WEEK: Geosteering: Part II – Data

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