Abstract
NLM field is located in Western Offshore of India, 46 km South-West off Mumbai city. The field was put full-fledgedly on production in the middle of 1994 after completion of necessary central processing and water injection facilities. Gas lift, as a mode of artificial lift, was anticipated in this field from the year 2000–2001, based on technological development plan of this field. The field was under development stage of planned development during 1994 and as such, laying of gas injection lines to every un-manned platform with high pressure compressors at process complex were planned to be executed just prior to 2000–01, but then the field production was caught off guard. At this period, water cut was expected to increase to 17%. However, water cut increased to around 26% within one year of regular production of the field, and by beginning of 1996, six wells ceased due to high water cut and six wells started flowing intermittently requiring frequent activation. This was due to reduction in wellhead pressure because of increased water loading. In the absence of artificial lift (gas lift) facilities, the field production started declining with the rise in water cut. Gas lift mode required laying of gas injection lines and required compression facilities based on latest reservoir simulation results in the changed scenario. Creation of such facilities normally takes 2–3 years gestation period after government level approval of revised scheme. In such situation, it was felt necessary to apply some innovative, immediate and very cost effective technique for arresting the decline of production from this field.
Some temporary common measures, like conversion of an existing 14" oil line between nearby HR field and N1 well platform (of NLM field) as gas injection line, were taken to bring in high pressure gas from HR to N1 to operate 3 ceased wells of N1 platform on gas lift, albeit, there were limitations on quantity and pressure of lift gas supply from HR. The said measures worked well to unload the water and maintained a regular uninterrupted production from the above wells.
On field data evaluation, it is observed that there is a small A-zone gas available above the oil zone in some parts of the field. However, the development of gas zone is scattered and limited. It has very poor open flow potential (about 55,000 m3/d). Studies further indicated that by drawing gas from this zone @ 10,000 to 12,000 m3/d, the zone potential will be exhausted within 6–8 months. But with optimistic view, one-year flowing life was envisaged for this zone. A detailed scheme, what was named as "auto-gas-lift" was designed and put into operation for N7, N8 and N9 ceased wells where overlying A-zone was developed. This resulted in additional oil production of about 1500 b/d.
Another innovative scheme of artificial lift at low cost was conceived in the form of "jet pump" using injection water as power fluid for some unmanned distant platform wells, where one or some platform wells are injectors. This mode was selected for ceased wells of N5, N7 well platforms. First trial with the available jet pump after improvisation was made on N7–7 well, which was highly successful with addition of 890 b/d production from this well. Based on this trial, subsequent auto gas lift completions in N7 platform were modified to install jet pump assembly by wireline. Both these innovative techniques were pursued simultaneously. The unique thing about jet pump was least cost since it had done away with the costly surface set-ups due to availability of high-pressure injection water at the platform. The jet pump assemblies were lowered in 6 more wells of N5 and N7 platforms, resulting in total average additional oil production of 1500 b/d.
By adoption of above listed measures, the field production decline was arrested to a satisfactory extent.
