A Successful Application of Fiber-Optic-Enabled Coiled Tubing With Distributed Temperature Sensing (DTS) Along With Pressures to Diagnose Production Decline in an Offshore Oil Well

摘要

In this paper, we present a field example where pressure and distributed temperature measurements enabled understanding of reservoir characteristics and fluid movement causing production hindrance in an offshore horizontal well. The field example comprises a horizontal well in the South China Sea that was completed as an openhole monobore oil producer using a slotted liner. The well began production with an initial oil rate of 1,800 bbl/d. Oil production quickly dropped to 1,000 bbl/d and gradually declined to 200 bbl/d. During this period, the gas oil ratio (GOR) steadily increased from 200 scf/bbl to 2,200 scf/bbl. To arrest production decline, a chemical treatment to remove suspected emulsions and polymers during drilling was conducted. Immediate post treatment, production increased to 2,200 bbl/d, but dropped dramatically and stabilized at pretreatment rates soon after. Formation of emulsions and asphaltenes were believed to be the cause of the production decline. However, with inadequate information, the diagnosis was inconclusive. Consequently, a fiber-optic-enabled coiled tubing string along with real-time bottomhole pressure and temperature gauges were used to acquire distributed temperatures and pressures of the entire horizontal section of the wellbore. Results of the pressure survey revealed that the well was receiving insufficient pressure support from the water injector, which, in turn, was causing gas cap expansion. The distributed temperature survey indicated excessive gas production from the toe of the horizontal section as a result of this expansion, thus limiting liquid production. The combination of gas rates with oil and water production has also created tight emulsions, further hindering production performance. It was concluded that the high gas production from the toe could not be selectively shutoff or controlled in the horizontal openhole slotted liner completion to perform an effective stimulation program and treat the tight viscous emulsions.