Sand on Demand: An Approach to Improving Productivity in Horizontal Wells Under Heavy Oil Primary Production

Abstract

The cold production recovery process, as it is practiced in Western Canada, is successful for vertical wells. Applications of cold production technology with aggressive sand production in horizontal wells, however, have been much less successful. This paper presents the results of experiments performed to assess the feasibility of applying cold heavy oil production with horizontal wells using less aggressive (i.e., controlled) sand production strategies. Specifically, the effects of slot size, confining stress, fluid velocity and sand grain sorting on sand production have been investigated. Preliminary results indicate that slot size selection is critical for establishing "sand on demand". For proper slot size selection, it is essential to know the grain size distribution of the sand; in particular, attributes such as the size of the coarsest fraction of the sand and the sorting (uniformity coefficient) of the sand. For example, it was observed in the sand production experiments that the critical pressure gradient for maintaining continuous sand production is much lower for well sorted sands than for poorly sorted sands. Ultimately, poorly sorted sands may require different criteria than well sorted sands for slot size selection. Flow rates are also crucial for managing sand production since a critical pressure gradient is required for initiating sand production and maintaining continuous sand production. The critical pressure gradient decreases as the slot width or confining pressure increases. Large permeability increases were observed in the sand production region. Persistent sand production led to the growth of a channel and/or the presence of a dilated zone which had an elliptic shape. Introduction Heavy oil production is becoming more important in Canada due to the depletion of conventional oil reserves. Western Canadian crude oil production is approximately 370,000 m3/d. Of this amount, nearly 75 % is composed of heavy crude and bitumen (including bitumen produced at mining plants). In situ heavy oil and bitumen production has more than doubled from 56,000 m3/d to over 165,000 m3/d in the last 25 years (Chugh et al. 1997; National Energy Board (NEB) 2008). Historically, recovery factors for conventional heavy oil primary production have fallen in the range of 1–5 % of the original oil in place (OOIP). However, the implementation of an enhanced primary production technique in the mid to late 1980s has raised recovery factors to between 5–20%. The new operating technique has been named "cold production" by Canadian producers. In the cold production process, sand is produced aggressively along with the heavy oil. This process has been successfully implemented in vertical (or slant or deviated) wells equipped with specialized pumping equipment (progressive cavity pumps). Nearly 50% (~ 37,000 m3/d) of western Canadian conventional heavy oil production comes from cold production areas in eastern Alberta and western Saskatchewan (Sawatzky et al. 2002). Horizontal drilling is a cost effective means of increasing output while unlocking reserves previously considered unrecoverable using conventional drilling technology. Applications of cold production technology in horizontal wells, however, have not been very successful. Horizontal wells produced under aggressive sanding conditions have required frequent sand cleanouts, which significantly increased the cost of the operations. A limited amount of sand production into horizontal wells, small enough to avoid plugging of the wells, may help to increase the permeability of the formation around the wells and lead to increased production rates. Therefore, a controlled sand production strategy aimed at enhancing the permeability of the surrounding formation could be an important factor in optimizing cold production in horizontal wells from unconsolidated heavy oil reservoirs.

Sand on Demand: A Laboratory Investigation on Improving Productivity in Horizontal Wells Under Heavy-Oil Primary Production—Part II

“…The viscosity and density of each heavy-oil sample were measured over a range of temperatures between 15 and 30 C. The measured viscosities of the two samples at 20 C were 3900 and 5100 mPa s, respectively, while the measured densities of the two samples at 15 C were 0.992 and 0.988 g/cm 3 , respectively. More-detailed information on the density and viscosity of this produced heavy oil is provided in Meza-Díaz et al (2008).…”

“…A description of the equipment can be found in Meza-Díaz et al (2008), with much more extensive details provided by Meza (2008). A photograph and schematic of the equipment used in the experiments are shown in Fig.…”

“…In order to monitor the effective-stress changes in the sandpack caused by sand production, two total stressmeters were designed. A description of these devices is given in Meza-Díaz et al (2008).…”

“…On the basis of previous results as described in Meza-Díaz et al (2008), and in more detail in Meza (2008), the ratio of slot width (SW) to the D 99.9 effective grain diameter (EGD) was chosen as the criterion for selecting slot widths in this study. The second row in Table 3 contains the values of the SW/ D 99.9 ratio for the sands evaluated in the study.…”

“…The oil-flow velocity through the slot in the experiments was matched to the oil-flow velocity through a slot under typical field conditions (Meza-Díaz et al 2008 ), respectively. The flow rates for the experiments were varied depending on the slot width to maintain these values for the slot fluxes (see Table 5).…”