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Collaborating Authors
Results
Abstract Obagi is a mature onshore oil field in the Niger Delta discovered in 1964 which comprises of mainly oil-bearing reservoirs with some reservoirs having large gas caps. Over the years, significant oil production has taken place in the oil rims of the reservoirs with large gas caps. Time-lapse fluid saturation evaluation using openhole well logs and cased-hole saturation logs (CHSL) established flushed oil zones and the existence of significant remaining gas columns in two gas cap reservoirs. Integrated reservoir studies identified watered-out wells that traverse these gas caps and are well placed to produce the gas zone with good clearance from the current water contact. In order to increase gas production potential from the Obagi Field at very low cost, a strategy of rigless intervention using coiled tubing for cement isolation and E-Line re-perforation to convert the watered-out oil wells to gas producers was adopted. Candidate wells for intervention were selected based on their location within the reservoirs, considering their proximity to the existing producers as well as the ease of connection to existing surface facilities. An intervention was carried out on OB-P1 by isolating the existing perforations via coiled tubing by setting a plug in the tubing above the watered-out zone, performing a tubing punch and circulating cement in the annulus. An E-Line re-perforation was then performed shallower in the R1 reservoir gas cap with a ceramic screen installed for sand control. A post intervention production test shows that OB-P1 has a gas production potential of > 250 kSm3/day (8.8 MMSCFD). This rate is constrained by damage (well still cleaning up) as well as mechanical skin due the completion type (ceramic sand screen) and the small effective wellbore diameter. Successful execution of three other planned conversion wells will replace, at least, one of the infill gas wells in the planned drilling sequence. This will result in a cost saving of about 65% of a new well.
Abstract In a brown field, the need to have a reliable well re-start and well activation method becomes increasingly important owing to the decline in reservoir pressure and possible heavy hydrostatic column after water breakthrough, leading to re-start and vertical lift difficulties. When this occurs, the well is said to be non-eruptive. The conventional method for solving this challenge is the use of gas-lift activation, which requires a gas source, compressors and scrubbers. Such equipments are currently unavailable on the Ofon field and a different approach to well activation had to be devised. The Ofon field development plan was in two phases. The second phase, which includes conventional gas-lift activation, was scheduled to commence seven years after the start of the first phase. No provisions were made for conventional gas-lift of wells in the first phase of the project. Unfortunately, the second phase of the project has been delayed for almost 10 years. Consequently, a new approach was devised to restart wells with low eruptivity and artificially lift wells which have lost eruptivity. The pseudo-gas lift method involves the use of a well with high GOR and high flowing well head pressure (FWHP) to lift another well through a surface pipeline called chicksan. The line is connected to the wellhead of the HGOR well via the swab valve on one end and the other end is connected into the annulus of the well requiring artificial lift. The implementation of this technique is simple and does not require additional equipment. This method has shown to be effective in cases where it is uneconomical to install a conventional gas lift unit, there are space constraints or there is delay in installing a conventional gas lift system as in the case of the Ofon field. An additional oil production of about 16 MMbbls has so far been obtained from the field with the use of this pseudo gas-lift method. [M = 10].