Refracturing Strategy for Sevensprings Oilfield in China Based on Geological and Engineering Characteristics

Abstract

Sevensprings oilfield is one of the oldest mature-flood fields with target stratum between 1000 and 1200m TVD in China with Strong permeability heterogeneity within the range of 0.01-50mD. Most of its wells have been fractured. But for now, the fractured wells have lost their power to maintain productivity. Early analyses show the wells have gained different production dynamics and the stress field around bottom hole was unclear after nearly 20 years water-flooding. Without a proper refracturing strategy, it still could not awake the wells properly. This paper presents a novel method to determine the refracturing strategy and the priorities of the candidate wells by comprehensive analysis, which considers reservoir properties, remaining oil distributions and induced stress fields. Application shows this method is effective and it can provide a reference for the analogous reservoirs to develop refracturing strategy. First we found out the basic situation of remaining oil and reasons for low-yielding of different wells under various fracture orientation and stratigraphic features through simulation. Combined with these two factors, we can divide the wells into different types which represented by residual oil distribution and location characteristics. After this, we obtained the induced stress field through marching the Waterflooding history. Through analyzing the hydraulic fracture steering angle and steering range, we can figure out the feasibility of steering fracturing to each well type. At last, we made a productivity simulation for each well type with corresponding feature models and fracture steering possibility. Based on this, we can develop the suitable refracturing strategy for every well type and gain the priorities according to the simulated productivity increment.The novel method established in this paper has been effectively applied in Sevensprings oilfield. Before this, there were more than ten well had been refractured, the average productivity growth rate was 34%, and some wells came to capacity drop because of incorrect treatment. Based on this method, we chose several candidates from more than 100 wells prepared to be refractured. And three of them have already been processed. All of them achieved preferable stimulation response. 3-3 shows an increasing fold of 3.85 from 2.57 t /d to 7.64 t /d. Shen-27 shows a daily production increase of nearly three times from 2.57 t /d to 7.64 t /d. Nowadays, larger-scale application was ongoing Application shows this new method to determine refracturing strategy and well stimulation priority is effectively. And it can provide a reference for the analogous reservoirs to improve their re-stimulation response.

Research on Refracturing Technology of Horizontal Wells Based on Dynamic Drainage Volume

“…Due to the failure of fracture initiation, sand filling failure and other problems in the production of primary fractured horizontal Wells, fractures may lose their conductivity. Therefore, refracturing is required to restore or improve the production capacity of horizontal wells (Giger, 1985;Vincent, 2011;Ren et al, 2015;Wan et al, 2019). At present, a large number of wells in the early development stage have been refractured (Siebrits et al, 2000;French et al, 2014;Fu et al, 2017;Athavale et al, 2019;Garza et al, 2019), and considerable results have been achieved.…”