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A dual lateral horizontal well was drilled on the Kneler structure of the Alvheim Field (offshore Norway) in 2015. The use of a newly processed 4D seismic dataset changed the original planned target for the main branch and led to justifying drilling the branch below an existing producer. The objective of the main branch was to target undrained oil below a stratigraphically compartmentalized segment. The Alvheim Field started production in 2008. The baseline seismic survey was acquired in 1996 and a 4D monitor survey was acquired in 2013. The 4D seismic data was used to estimate the movement of the oil water contact, and 4D difference geobodies were benchmarked against production data directly, giving high confidence in the estimates. The 4D difference geobodies were integrated in the history matching process. A lower zone infill target below an existing upper zone producer was identified as the result of the multidisciplinary data integration. The lower zone has excellent pressure support via the large Heimdal aquifer system while the upper zone producer has limited pressure support and has historically produced at low rates. Pre-drill reservoir simulation studies indicated a benefit in enabling cross-flow between the two zones. The drilling results showed oil as predicted by the 4D seismic data. However, the upper zone was thicker than expected. A thin oil column was found in the lower zone before drilling into water, again confirming the 4D seismic interpretation. As the lower zone target was smaller than expected, the main value of the branch was refocused towards enabling optimal cross-flow. The pre-drill reservoir models were updated pragmatically and studies were done to optimize the lower completion, e.g. deciding the optimal cross-flow rate, production and injection intervals and how to use inflow control devices to assist the clean-up of all zones. The clean-up went as planned in November 2015 and a 20 bar drawdown was achieved across the injection interval of the branch. The branch was produced for 40 days before shut-in to act as a cross-flow injector. Pressure interference data indicated a successful clean-up of the injection interval. The cross flow well has showed to work as intended giving an increased oil rate of around 4000 stb/d. A cross-flow injector can be a cost effective solution for partly segmented compartments close to strong aquifers. To the knowledge of the authors, no example of this type of cross-flow injection has been documented in the literature.
A dual lateral horizontal well was drilled on the Kneler structure of the Alvheim Field (offshore Norway) in 2015. The use of a newly processed 4D seismic dataset changed the original planned target for the main branch and led to justifying drilling the branch below an existing producer. The objective of the main branch was to target undrained oil below a stratigraphically compartmentalized segment. The Alvheim Field started production in 2008. The baseline seismic survey was acquired in 1996 and a 4D monitor survey was acquired in 2013. The 4D seismic data was used to estimate the movement of the oil water contact, and 4D difference geobodies were benchmarked against production data directly, giving high confidence in the estimates. The 4D difference geobodies were integrated in the history matching process. A lower zone infill target below an existing upper zone producer was identified as the result of the multidisciplinary data integration. The lower zone has excellent pressure support via the large Heimdal aquifer system while the upper zone producer has limited pressure support and has historically produced at low rates. Pre-drill reservoir simulation studies indicated a benefit in enabling cross-flow between the two zones. The drilling results showed oil as predicted by the 4D seismic data. However, the upper zone was thicker than expected. A thin oil column was found in the lower zone before drilling into water, again confirming the 4D seismic interpretation. As the lower zone target was smaller than expected, the main value of the branch was refocused towards enabling optimal cross-flow. The pre-drill reservoir models were updated pragmatically and studies were done to optimize the lower completion, e.g. deciding the optimal cross-flow rate, production and injection intervals and how to use inflow control devices to assist the clean-up of all zones. The clean-up went as planned in November 2015 and a 20 bar drawdown was achieved across the injection interval of the branch. The branch was produced for 40 days before shut-in to act as a cross-flow injector. Pressure interference data indicated a successful clean-up of the injection interval. The cross flow well has showed to work as intended giving an increased oil rate of around 4000 stb/d. A cross-flow injector can be a cost effective solution for partly segmented compartments close to strong aquifers. To the knowledge of the authors, no example of this type of cross-flow injection has been documented in the literature.
This paper describes the analysis, test and design work to deliver an optimum lower completion for a tri-lateral well, by integrating autonomous and passive inflow control devices (ICD), in the Alvheim field offshore Norway. Chemical tracers, permanently installed in the completion, enabled the evaluation of inflow performance in each lateral. This continues to give valuable information to assess whether the tri-lateral completion is performing as predicted, improves reservoir characterisation and guides reservoir management decisions. In 2015, both passive and autonomous inflow control devices (AICD) were tested in the laboratory with Alvheim fluids at reservoir conditions. The experimental flow testing, reported in this paper, demonstrated that the AICD chokes gas more efficiently than the passive ICD, but also that the strength of the AICD were lower than expected a priori. The experimental results were used to model the AICD correctly and establish a lower completion strategy as follows: where the well was close to the overlying gas cap, AICDs should be used, while passive ICDs with variable strength were to be used elsewhere to optimise the inflow. Steady-state inflow modelling was performed before the drilling operation and updated accordingly with the as drilled information. The lower completion design for each branch focused to get what was estimated to be an optimal inflow based on oil volume in place. A key uncertainty in the design work was whether shaly zones along the wellbore would creep/collapse with time and act effectively as packers or not. The lower completion covered around 7 km of reservoir penetration in the three branches, and 15 unique oil tracers were installed to evaluate the clean-up and the inflow profile along the well. The well started producing in May 2016 and downhole flow control valves enabled a successful clean-up, as confirmed by oil tracer responses. In addition, a restart tracer sampling campaign was done after a 12-day shut-in, in August 2016, and this formed the basis for a "chemical production log". The tracer based inflow interpretation is compared quantitatively with the model predicted inflow and qualitatively to the tracer responses seen during the clean-up. This gives valuable feedback to the completion design, and assist in understanding the various degrees of pressure support and if the shaly reservoir sections have creeped/collapsed or not. The well has exceeded pre-drill production expectations, with an average oil rate of 3375 Sm3/d (21240 stb/d) during the first production year. This is a consequence of higher than expected NTG, but is also partly a result of the lower completion design, where the focus has been to optimize the lower completion such that the whole well contributes, from the heel to all toes. To the knowledge of the authors, this is the first well in the world with a lower completion integrated with AICDs, ICDs and chemical tracers.
Summary In this paper we describe the analysis, test, and design work to deliver an optimal lower completion for a trilateral well by integrating passive and autonomous inflow-control devices (ICDs) (AICDs) at the Alvheim Field offshore Norway. In 2015, both passive ICDs and AICDs were tested in the laboratory with Alvheim fluids at reservoir conditions. The experimental flow testing demonstrated that the AICD chokes gas more efficiently than the passive ICD. The experimental results enabled correct modeling of AICDs in both the reservoir-simulation model and the simpler steady-state inflow model. The following lower-completion strategy was established for the new well: Where the well was close to the overlying gas cap, AICDs should be used, whereas passive ICDs with variable strength were to be used elsewhere to optimize the inflow. During the drilling phase, the steady-state model was updated with the as-drilled information; the lower-completion design for each branch focused on obtaining what was estimated to be an optimal inflow depending on the oil volume per drainage area. A key uncertainty in the design work was whether shaly zones along the wellbore would creep/collapse with time and act effectively as packers. The lower completion covered 7 km of reservoir penetration in the three branches, and 15 unique oil tracers were installed to evaluate the cleanup and the inflow profile along the well. The well started producing in May 2016 and a successful cleanup was confirmed by oil-tracer responses. In August 2016, a restart-tracer-sampling campaign was performed after a 12-day shut-in, and this formed the basis for a “chemical production log.” The tracer-based inflow interpretation was compared quantitatively with the model-predicted inflow and qualitatively to the tracer responses seen during the cleanup. The comparison confirmed that the lower completion works as initially planned. The interpretation further indicated that the upper zone has a lower degree of pressure support than the lower zone, and that the larger shaly sections have creeped/collapsed and act as packers. The well has exceeded predrill production expectations, with an average oil rate of 3375 std m3/d (21,240 STB/D) during the first production year. A large part of exceeding the predrill expectations is attributed to the lower-completion design, where the focus has been to optimize such that the whole well contributes, from the heel to all toes.
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