The management of residual oil on drilled cuttings poses a major environmental consideration for offshore drilling. Often the methods employed are dictated by regulatory regimes. Where ‘zero discharge’ is specified by regulators then ‘skip and ship’ or ‘cuttings reinjection’ become the primary technologies available. In regulatory regimes where a degree of marine discharge is permitted, the cuttings driers or offshore thermal desorption technologies are used to reduce the % amount of oil on cuttings prior to discharge to the ocean. Conventional cuttings driers, the technology currently used in Ghana, typically give 3% or more of oil on cuttings by weight of cuttings. Though this is relatively low and tolerable in some jurisdictions, both legislators and operators have a commitment to further reduce discharges in a progressive manner. Most of Ghana's oilfields fall in deepwater areas and cuttings re-injection methods are not being actively considered in the near term due to less mature deepwater technology and cost. The offshore treatment using offshore thermal desorption offers an alternative method to treat drilled cuttings offshore and reduce the oil concentration on cuttings to typically less than 0.5% by weight prior to marine discharge. An overview of the method is however offered in this paper. The Skip and ship methods where cuttings are shipped onshore and treated to remove oil on cuttings before being disposed of onshore, is used in other deepwater areas. Special offshore cuttings handling equipment plus a marine and road logistics network as well as onshore treatment infrastructure are required to support such activities. This paper will look at the relative merits of offshore cuttings treatment by thermal desorption technology compared to skip and ship methods. It will consider the merits of each method in the context of projected Ghana drilling activity, onshore infrastructure requirements and other considerations.

This case study describes the approach taken when drilling an 11 5/8-in. hole section through a salt formation on the Chinarevskoye field in the West Kazakhstan Oblast region where high-intensity brine influxes and subsequent flow had been encountered. The intensity of the brine flow, when encountered, had ranged from 5,000 to 6,000 L/min at an equivalent kick density of 2.2 SG, and it is believed to be among the most intense brine flow experienced in the world during drilling operations. Standard well control measures proved to be inefficient because of the narrow margin between pore pressure and fracture pressure gradients. Several techniques were applied to combat such influxes in a safe manner with minimum associated nonproductive time (NPT). The high-pressured formation in this hole section is associated not only with brine influxes, but also with losses and gas increase scenarios. As a result, the company adopted unconventional drilling techniques with a combination of planned flow-while-drilling (FWD) and mud-cap drilling techniques to reach total depth (TD). These two techniques created a viable and cost-effective solution to mitigate such challenges, helped the company to drill to the planned section TD, and consequently complete the well within the defined authorization for expenditure (AFE) without associated NPT. The paper will cover and emphasize techniques, along with details on running casing and cementing the hole section, which required an unconventional approach for success. The paper will also briefly outline the equipment used, such as rotating control devices (RCDs), a choke manifold, and a separator when drilling this section and their limitations. Despite the complications, the well was successfully drilled, and this experience provided an opportunity for learning. The marked improvements in well control, loss management, and cementation displayed that combining knowledge and experience can reduce the negative impact on well costs when drilling similar cases.