Changing the Injection Water on the Blane Field, North Sea: A Novel Approach to Predicting the Effect on the Produced Water BaSO4 Scaling Risk

Abstract

The Blane Field, North Sea, has one injection well and two production wells and is tied back to the Ula Field platform. The original scaling risk assessment was based on injection of platform produced water (PW) with minor seawater (SW) (~90:10 PW:SW). However, after injection of 25:75 PW:SW for only 6 weeks, a change in operational circumstances on the Ula Field meant that only 10:90 PW:SW injection water could be supplied for the next 18 months. There was a risk that this might result in unmanageable BaSO4 scaling conditions in the production wells but the alternative would be to cease injection, leading to reservoir pressure decline and loss of oil revenues. The need for a rapid decision negated the use of reactive transport reservoir simulations to predict the future BaSO4 scaling risk under the new injection scenario so a novel, alternative approach was adopted. A history matched ECLIPSE model served as the basis for predicting the types of water entering the production wells over time and their rates. A 1-D reactive transport model was then used to predict the Cl, Ba and SO4 composition of these waters after accounting for the effects of reservoir reactions. These results were integrated in a spreadsheet to provide predictions of Cl, Ba and SO4 concentrations in the produced water from each well over time. The results for future injection water scenarios indicated that the scaling risk would increase over time in the wells but, due to deposition of BaSO4 and CaSO4 in the reservoir, the BaSO4 scaling risk would be manageable even allowing for uncertainties associated with this approach. Based on these results, and those of associated studies, a decision was made to continue water injection resulting in avoidance of loss in oil revenues. This novel scaling prediction approach may be useful on other fields where reactive transport reservoir simulations may not be possible.

Selection of Scale Control Strategy on a Sub Sea Developed Field in the North Sea and How 6 Different Companies Contributed

“…This showed that it is the response of A04, which would be critical should changes in injection water composition be required again in future. Due to the high Ca content of the PW and deposition of CaSO 4 in the reservoir, it was also predicted that if only 15% PW could be added to the injected seawater, the peak SR BaSO 4 for A04 could 1 . Many of these uncertainties would also arise had reactive transport reservoir simulation been used to assess the scaling risk (e.g.…”

“…The mineralogy of the reservoir sandstone has been published previously. 1 The production wells have perforated sections designed to intersect multiple layers and are completed with gas lift facilities to aid production at high water cuts. The injection well was perforated to allow injection into the oil-leg and top of the water-leg.…”

“…When the production dropped below 12 000 bbls per day, gas lift was started and the production increased to above 14 000 bbls per day. During the time period this paper discusses, no water 2 2.10 C 1 28.50 C 2 4.52 C 3 5.26 IC 4 1.72 nC 4 4.31 iC 5 2.23 nC 5 2.99 C 6 4.28 C 7 3.56 C 8 3.71 C 9 2.98 C 10ϩ 33.48 Total 100 breakthrough was observed in the Blane production wells therefore the dominating produced water chemistry from the Blane reservoir was not known. The water chemistry presented in this paper was measured on samples from DST´s taken before production started up.…”

Application of Multi-rate Well Tests to Scale Management

“…Linear regression was applied to the MRT Cl and SO 4 analyses and this indicated that the low pressure zone was the IDS and that seawater breakthrough had occurred in this zone (see Figure 8). Water is likely to entering the well in the IDS zone from multiple flow paths, with each producing either pure formation water, pure reacted seawater, or a mixture of seawater and formation water close to equilibrium with respect to BaSO 4 ±SrSO 4 (McCartney et al, 2010). Also, the seawater fraction for each path may be different and the clay content of these flow paths may vary within the range discussed above.…”