Gas-Influx Events in a Deep Water Exploratory Well: A Field Case History

Abstract

Several gas-influx events have occurred during drilling ESS-107, an exploratory well in a 1286 m of water depth offshore location in the southeast coast of Brazil, state of Esp rito Santo. The 9 5/8" casing was set at 3804 m for drilling the final 8 1/2" phase of the program. Then, a sequence of gas-influx events affected substantially the overall performance of the drilling activity. The first influx occurrence was observed while drilling at 4719 m and it was initially diagnosed as over-pressured. Consequently, after using the driller's method to remove the gas, the mud weight was increased from 11.3 to 12.5 lbm/gal. After that, some other well control incidents happened in sequence while drilling from 4719 to 4826 m. Despite the suspicion of a fracture breathing formation phenomenon, the mud weight was increased up to 13.7 lbm/gal without putting an end to the flow of gas into the well. In addition, as water based mud (WBM) was routinely flowing through the choke and kill lines mixed with gas, the low temperature of the environment close to the seafloor triggered the formation of hydrate. So, both kill and choke lines were plugged, which was indeed the first occurrence of hydrate formation in deep water while drilling in Brazil. The present study analyzes the influxes based on all available data, such as daily drilling reports, daily drilling fluid reports, final well report, mud logging data, pressure while drilling (PWD) data, etc, to determine if the fracture breathing formation phenomenon was really the driven mechanism. The control procedures used are also discussed and evaluated. Finally, a proposal is presented to improve the overall drilling performance for the succeeding wells in the area. Introduction The EspÍrito Santo basin is located alongside the coast of the state of EspÍrito Santo and the southern coast of the state of Bahia, in the southeast coast of Brazil. As showed in Figure 1, this sedimentary basin borders at south the Campos basin, which is the most important oil province in Brazil. Its sediments can be found both onshore and offshore, covering 123,130 km2, out of which 17,900 km2 are onshore and another 52,860 km2 are shallower than 400 m. In spite of being the pioneer in terms of the exploratory offshore activity in Brazil, most of the producing oil fields in the Espirito Santo basin are onshore. In fact, the offshore portion of the basin has been showing good potential for the gas production. The fields of Cangoá and Peroá, which are gas producers discovered in 1988, are illustrative examples. The sandstones of the Urucutuca formation, which were deposited in different geotectonic scenarios, are usually the main offshore goals in the Espirito Santo basin. In particular, the turbidite sandstones of the Urucutuca formation are attractive because of their potential for gas production. Departing from this exploratory perspective, the well ESS-107 was planned to be drilled on a 1286-m of water depth location at the block BES-2, south of Peroá field and at about 60 km from the coast of Brazil, as indicated in Figure 2. The drilling operation was executed conventionally in accordance with the normal standards of performance until reaching the end of the 12 1/4" phase. The 9 5/8" casing was set at 3804 m and a formation integrity test (FIT) was performed, limited to 13.8 lbm/gal. While drilling ahead with the 8 1/2" bit at 4719 m, total mud volume augmented suddenly and a pit gain of 10 bbl was noticed. Simultaneously, pump pressure dropped down about 250 psi. Then, the drilling crew performed a flow-check that expanded the pit gain to 25 bbl. The well was shut in and conventional (driller's method) kill operations commenced. After raising the mud weight from 11.3 to 13.2 lbm/gal with an intermediate step at 12.5 lbm/gal, the well, which appeared to be killed, was opened and found to be static. The drilling operation was resumed, but after circulating bottoms up subsequently to connections, gas peaks and pit gains were registered. In spite of further increases in mud weight to a maximum of 13.7 lbm/gal, the entrance of gas into the borehole could not be prevented.

Formation Damage History in the Mature Fields of Campos Basin Offshore Brazil

“…In March 2001 the first occurrence of hydrate formation while drilling was reported in a deep water well of Espírito Santo Basin, close to CB. Gas influxes due to fracture breathing formation phenomenon were the primary cause of hydrate formation 29 .…”

Opening New Exploration Frontiers With The Micro-Flux Control Method For Well Design

“…Lage et al 41 reported a case in which several gas influx events occurred during the drilling of an offshore exploratory well in 1286 m of water off the southeast coast of Brazil. Despite the suspicion of a fracture breathing formation phenomenon, the mud weight was increased from 12.5 up to 13.7 ppg, without putting an end to the flow of gas into the well.…”

Estudo da solubilização do metano no elemento de barreira de fluido de perfuração de base n-parafina

“…5 -Evolução dos simuladores de controle de poço (Chagas, 2016) Figura 4. 1 -Curva de avanço da perfuração (adaptado de Lage et al, 2002) _________ 53 Figura 4. 2 -Perfil de pressão previsto na perfuração (adaptado de Lage et al, 2002) __ 54 Figura 4.…”

“…1 -Curva de avanço da perfuração (adaptado de Lage et al, 2002) _________ 53 Figura 4. 2 -Perfil de pressão previsto na perfuração (adaptado de Lage et al, 2002) __ 54 Figura 4. 3 -Ganho de lama em função da RGL para fluido aquoso _________________ 56 Figura 4.…”