This paper summarizes the results and learnings from the Autonomous Inflow Control Device (AICD) deployment and installation in multiple heavy oil fields in south Oman, allowing for swift utilization in other fields with similar characteristics. Those AICDs were mainly deployed and tested in those oil fields comprehensively, in horizontal producers, and the results were supported by rigorous lab tests was conducted to understand their behavior. This paper is a continuation of the work in reference [1].
In recent decades, horizontal drilling for producing wells became a widely known and used technology, this is due to the fact they improve the overall recovery, efficiency of production, drainage of the reservoir, as well as delay unwanted fluids (e.g. gas & water). However, this solution was not perfect, as due to highly fractured and heterogeneous reservoirs, premature water and gas production can and will take place, causing remaining oil to be bypassed, and hence, reducing the reservoir's recovery and eventually the profitability [2]. In south Sultanate of Oman, many fields have been developed with the use of the horizontal well technology, but together with its advantages, the geological nature of the formations and the physical properties of the produced fluids, have introduced important challenges regarding production optimization.
One of the assets in question comprises of naturally fractured carbonate reservoirs drained through long horizontal open-hole completions. It has been developed with water flood and GOGD system. The main production optimization challenge faced for that asset is the fracture-dominated inflow, which leads to either high water or gas production. On the other hand, another asset where the trial took place comprises of shallow sandstone reservoirs of heavy oil, with strong bottom aquifers and high level of reservoir heterogeneities; fractures, faults and high permeability streaks are characteristic of these reservoirs. A horizontal well usually has a much higher capacity–as compared to a vertical well–for producing fluids at the same drawdown, hence, when talking on critical rates that do not disturb the oil-water-contact, horizontal wells will definitely have a higher critical rate than those of vertical wells, but even so, the capacity of moving fluids are bigger, causing faster movement of bottom water towards the horizontal well regardless [3].
Another field of the trial fields had produced heavy oil, with viscosities in the range of 600 cP to 1000 cP. The permeability is variable and in the range of 100mD to 10D. This makes the mobility ratio very favorable to water production. Some wells have started production with less than 10 % WC, but a sudden increase of WC has been observed up to above 90 %. Most of the wells have been completed with inflatable packers (EZIPs), creating 2 to 3 segments at the horizontal reservoir section. The AICD technology is suitable for being applied in this case of very low oil mobility and segments at the sand-face. The last trial field comprises of multi-stacked reservoirs, isolated by shale barriers, with production potential of oil from two main layers. The oil is light, ~ 42 API and 0.9 cp viscosity. Around 13 wells are closed-in due to various reasons including high water cut and low productivity. This field is producing since 1998 from 9 stacked reservoir zones-commingled, which provides a challenge to production allocation. Performing Production Logging Tests–PLTs-have not helped to improve the allocation issues. Water shut off is challenging when it comes to the point of deciding the zone required to be closed. Mechanical water shut off is an option to choke back the non-allocated water zones and allow more oil production. Although this field does not include horizontal wells, the total perforated length of the proposed well and the hydraulic natural isolation between the producing zones makes the application of the technology attractive for this field.
An interventionless/wireless technology, which promotes uniform production along the entire length of a horizontal well, delaying the production of unwanted fluids (water or gas) from high productivity zones along the well path and promoting increased oil production from other compartments of the formation, would definitively represent a key aspect of the production optimization for these Petroleum Development Oman fields.
