We are looking for solutions, methods and/or technologies that can prevent fracture related losses:
The main challenge to drill in a depleted reservoir is to avoid the loss of drilling fluid to the surrounding formation. The drill operators see a ‘lost circulation’ situation when there is less drilling fluid coming up the annulus of the borehole than is pumped through the drill-string.
Lost circulation often occurs in wells with weak points that can be present in a depleted reservoir such as in transitions zones between shale and sandstone layers or when drilling mechanically weak or naturally fractured formations (e.g. paleosols/coals). When the new borehole reaches such a zone there can be an unexpected drop in pore pressure (and thus lower “fracturing” pressures) or the lithology transition itself represents a weak point where fluid loss can occur as a result of either induced fracturing or loss into existing fissures/channels (see Figure 1).
When lost circulation occurs, sealing the loss zone is necessary. Sealing normally involves adding a blend of carbonate particles with a broad particle size distribution to the drilling fluid, either in small volumes as a preventive measure or as a massive “pill” to cure losses by sealing off fractures and other openings in the formation. In addition to carbonate a variety of other materials exists including mica, cellophane, cement or bentonite based plugs.
Experience shows that being able to arrest incipient fractures/loss incidents early and limit additional losses gives a better chance for being able to cure/heal losses successfully and continue drilling without requiring methods that can lead to loss of the well and sidetracking. In general there is a greater potential for serious consequences with bigger loss rates and larger loss volumes/time on losses.
Statoil is therefore looking for innovative solutions that can quickly cure a lost circulation incident and allowing the operator to resume drilling.