Summary
Excessive sand production, uneven recovery of reserves throughout the length of a horizontal well and early water and gas breakthrough are deemed to be the main problems while developing poorly consolidated terrigenous fields with contact reserves. Assessment of feseability of possible completion systems (gravel packing and autonomous inflow control devices were chosen for implementation) is necessary at the pilot stage of the project. Pilot wells shall be monitored at each stage including development, recovery, observation over the dynamics of water and gas breakthrough processes. The use of traditional PLT methods is not always technologically feasible and cost-effective. This article describes the experience of using stationary of intelligent inflow markers for permanent monitoring for the purposes mentioned above.
Over the last years, operators get to think about hard-to-recover reserves in poorly consolidated reservoirs of Pokur formations saturated with highly viscous oil and complicated by underlying aquifers and gas capsmore frequently. Low level of knowledge about the reservoir makes it difficult to select an efficient completion technology for ERD wells.
This paper describes a successful experience of construction and "complex" completion of wells, with application of various types of inflow control devices at the North-Komsomolskoye field.
To solve the challenges of the North-Komsomolskoye field and to find an efficient development system, a decision was made to drill ERD wells with 1,500 and 2,000 m long horizontal sections, which, considering the vertical depth of ~1,120 m, already represents a challenge in terms of drilling and completion string running operations.
The complicating factors dictate the necessity to select a completion system which effectively prevents sand production and limits the unwanted fluid inflow into the wellbore.
The extensive calculations of drilling and completion running processes resulted in application of heavy-wall drill pipes with unusual for Russia 114.3 mm (4.5″) high-torque threaded connections used for drilling and completion assemblies running processes. The liner running operations are carried out using a power swivel: a device for running string (RS) rotation independently from the liner. Drilling of long horizontal sections is carried out with oil-based mud to significantly decrease the risks related to wellbore placement and stability issues.
Considering the reservoir heterogeneity, a multizone completion system is used, with swellable packers. To enable packers’ activation, ensure proper displacement of OBM from the wellbore and reduce risks of counterflow emulsions formation, the well is displaced to brine with the use of multi-composition spacer fluids and a washpipe to ensure circulation via the filter liner shoe.
One of the completion stage constituents is the laboratory-based selection of autonomous inflow control devices and valves along with validation of sand filters. The successfully performed completion stage in long horizontal sections provided very good results during wells operation:
Higher flow rates vs. previously drilled wells. No water/gas breakthrough vs. wells completed only with filters. Absence of significant production of solids.
Well completion using technology enabling to improve performance and life time is an important objective in the development of PK1 productive reservoir of North Komsomolskoye field. The main challenge of the development of this productive horizon lies in the fact that the reservoir is shallow (1,120 m TVD) and consist of poorly consolidated sandstone, which results in massive production of solids during operation. In addition to that, proximity of GOC and WOC together with high oil viscosity in reservoir conditions results in early gas and water breakthroughs when using standard completion technology.
Basic PK1 formation characteristics could be found in Table 1.
Remote location of the field and impossibility to use all-year-round road transport of materials, equipment and personnel are additional operating problems which had to be resolved to ensure that the project is delivered successfully and without extra costs.
Main questions which the project team had to deal with: What is the long-term solution to limit solids production at target drawdown to a level that would be safe for pumps and surface facilities?How to prevent early water and gas breakthroughs?How to drill a long horizontal section in poorly consolidate rock without any incidents knowing that previously several wells were lost in this zone due to well caving during drilling?
To tackle these problems, we chose a completion technology for the open horizontal section using screens equipped with autonomous inflow control devices (AICD) and inflow tracers. To ensure sand control, we injected gravel packing in the annular space between the screens and the open well bore. In addition to that, we built a 1D rock mechanic model to calculate well bore stability.
During the project execution we drilled 2 long horizontal sections without any incidents; tested completion technology with gravel packing (well A) and without gravel packing (well B); obtained the planned oil inflows; confirmed that the approaches adopted can be successfully used in the Full Field Development.
Given all the particular features of the field and the well design, this operation can be rightly considered one of the most complex onshore operations that have been performed in the Russian Federation.
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