Field Experience Leads to Effective Bypass of Formation Damage Caused by Asphaltenes Deposition and Improves Production from a Naturally Fractured Carbonate Oil Reservoir

Abstract

The largest active onshore field in Western Europe produces crude from 20 long horizontal wells from a naturally fractured carbonate reservoir. The produced crude deposited asphaltenes in tubing, openhole sections, and slotted liners. Over time, the deposition became so severe that it involved the reservoir fractures, affected well productivity, and caused a premature fieldproduction decline. Removing the formation damage, therefore, became a priority for appropriate field management.The injection of asphaltene inhibitors at packer depth reduced asphaltene deposition in tubing but did not protect the long openhole or the natural fractures from plugging. Bullheading or coiled-tubing (CT) solvent treatments were frequently performed with limited benefits.In 2009, an extensive asphaltene cleanout campaign was performed with more aggressive solvent treatments, covering almost 70% of producing wells. Continuous post-treatment-analysis improved the stimulation effectiveness and optimizing the dissolving fluids led to a production increase per treated well of 500 to 3,500 bbl crude per day. Unfortunately, the treatment techniques applied did not allow sustained production increase unless well interventions were frequent, up to bi-monthly.To reduce the treatment frequency, an emulsified-acid treatment was performed. The innovative emulsion, where acid was emulsified in solvent, provided a delayed acid reaction and allowed live acid to penetrate deeper into the formation. This allowed the flow pattern to be changed in a way such that the asphaltene deposition was slowed down, and the high well production was sustained over a prolonged period. This paper describes the history of the treatment methods, the extensive asphaltene-cleanout campaign performed, the post-job analysis, stimulation-treatment improvements based on field experience, and the final novel application of an emulsified-acid treatment that sustained a prolonged production gain of more than 10,000 BOPD and recovered initial well productivity.

Removal of Plugged Asphaltene in a Reservoir by Earthquakes

“…The severe asphaltene problems of Field 'M' are similar to those of other cases in which asphaltene problems were reported (Leontartis and Mansoori 1987;Garcia et al 2001;Kokal et al 2003;Strippoli et al 2010;Al-Qattan et al 2012). However, a unique feature of this case is that frequent earthquakes have hit this field, and the reservoir has responded positively to certain earthquakes in terms of oil production rates and flowing wellhead pressures.…”

“…The problems related to asphaltene deposition in Field 'M' are presumably comparable with those reported in the literature (Leontartis and Mansoori 1987;Garcia et al 2001;Kokal et al 2003;Strippoli et al 2010;Al-Qattan et al 2012). However, a unique feature of this field is that it has been struck by frequent earthquakes, and the reservoir has responded to certain earthquakes.…”