The Lloydminster, Alberta/Saskatchewan, heavy oil region has necessitated our industry1–2 to re-evaluate traditional methods used in sand retainment and mechanicalmechanisms. 3
Primary well methods of gravel packs and preformed liners proved ineffective in heavy oil wells. Operators, in recent years have found that in primary and thermal recovery applications, wire wrapped screens outperformed the more expensive traditional methods.
Successful screen installations, sized to the theory of partial sand retainment, generally use slot sizes much larger than those of conventional means.
Research and development of sand retainment sizing and mechanical mechanisms in heavy oil employment has advanced new screen installation/reinstallation techniques with associated running equipment which is proving not only production efficient but more importantly, cost effective.
Over the years there has been many attempts made to formulate a successful, economical method of heavy oil well sand retainment. Wells in the Lloydminster, Alberta/Saskatchewan area have a A.P.I. gravity of 12 degrees or less measured at 15.5 degrees celsius.
The sand production related to primary heavy oil wells is areal and spotty. Initial sand retainment installations proved ineffective and induced plugging. Sand retainment forms became objectionable to oil operators in the region.
Secondary recovery of heavy oils by the steam process, (continuous injections and cyclic huff and puff), soon became widely used. Formation sand in many of these thermal projects was produced at such a rate that development of a sand retainment process became an economic requirement.
The ultimate and retainment form needed to be durable, minimize pressure drop and be economically attractive.
Through the process of elimination, it was found that by hanging the largest outside diameter, wire wrapped, stainless steel screen, through an open hold interval retainment, the best results were achieved.
This theory of partial sand retainment, pertaining to steam stimulation had proven economical. This theory, at present, is being applied to some primary wells with a predicable degree of success.
Because of their ease of installation, pre-packed liners were initially utilized in thermal projects within the Lloydminster region. The process either plugged or produced sand through erosion and/or weight loss due to matrix cement deterioration.
An under reamed, open hole, gravel pack is theoretically optimum in minimizing pressure drop, therefore mazimizing production rates. Gravel packs and pre-packed liners are two (2) step sand retainment method therefore being less specific than sizing one (1) step method, such as wire wrapped screened liners.
Maximum flow rates were achieved in wells with optimal pack permeability. From this information the philosophy of 'tear drop effect', (Figure 1), sand sizing, complimented by gravel pack sand sizing by resieving was evolved. By sieve analysis of many produced and cored formation sand samples from the area. A pattern emerged. The majority of the sane particles were sorted towards finer grain sizes. The gravel pack san that best reflects this curve is grade4.