Consistent rheology is crucial for the successful construction of a deepwater oil/gas well. Oil wells with water depths greater than 5,000 ft are an industry norm, with temperatures at the seabed close to 40°F. There is a continuous need to drill with products that are environmentally-acceptable and yet technically capable. At cold water temperatures, invert emulsion fluids (IEFs) typically exhibit a significant increase in rheology, becoming noticeable in the riser after static periods. To break circulation after static periods or while circulating, the high rheology of the IEF necessitates high pump pressures to initiate or maintain circulation. High pump pressures mean high equivalent circulating densities (ECDs) at the bottom of the well, increasing the probability of losses. Fluid losses in deepwater wells can be costly, considering the difficult logistics.

Traditionally, thinners are added to the IEF to pre-empt an increase in rheology in cold waters and to help minimize the ECD. This entails precise control over the rheology of the IEF along the depth of the well, especially in the hotter regions. Failing this can result in the poor suspension of barite or drilling cuttings. A desirable IEF has a consistent rheology from the platform to the riser and to the bottom of the well.

Wagle et al. (2012) describe an organic rheology modifier (ORM) that delivers a consistent rheology to the IEF in temperatures ranging from 120 to 400°F at 18,000 psi. Taking this a step further, an additive to the ORM (AORM) was developed that synergistically interacts with the ORM in the IEF. The IEFs formulated with the AORM and ORM in three base oils common to deepwater operations demonstrated the following:

  • Consistent rheology from 40 to 150 to 350°F at 15,000 psi and higher.

  • Improved suspension to barite particles.

Furthermore, both the AORM and the ORM passed the stringent toxicity and biodegradation required for use in the North Sea.

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