The demand for the ideal perforating product for cold production (CP) is a vigorous quest. Numerous products have been introduced into this market. The success of these products, though, has been poorly tracked. The suggested practices contained herein are the summation of (and perhaps an extrapolation of) the most popular practices of a wide range heavy oil producers, operating in a large geographical area. Admittedly, the assumption that heavy oil is one great big homogeneous reservoir and should be subjected to all the same completion techniques (including perforating products and perforating techniques) is without merit. Given the limited data and actual science we have to work with, when choosing those techniques, that is precisely the assumption made. Even with what might be described as poor science and bad engineering,¹ the success of CP (in which aggressive perforating is a key component) is indisputable. The techniques and products used in CP are constantly evolving and as a result are slowly being experimented with in other types of reservoirs.

Sometime in the early 1950’s a field trial was attempted using plastic coated walnut shells dump bailed into an open hole completion in hopes of controlling sand inflow. The trial failed. So did many other similar trials and experiments (including but not limited to sand screens, fire flooding and sonic pumps). The pioneering spirit/attitude/practice of working with what you have and try, try, try-fail, fail, fail is still the state of the art in heavy oil production. In fact without it, cold production would not now be acceptable practice. The attitude of the production and service sector staff is as much as a key component to CP as the right type of completion, the right PCP pump or the right perforating product.ⁱ The committed cold producer therefore is continually learning (i.e. failing).

Perforating charges

The modern jet charge came from the same technologies used in the development of armor piercing ammunition between the First and Second World Wars. To perforate casing the charge forms a jet of particles traveling at a velocity which enables it to pierce the casing, cement and the formation. Figure 1 illustrates the sequence of forming a jet and lists the components of the charge. Figure 2 demonstrates the effects of the geometric variables. It is easy to see the limitations of this technology when placed in the confines of a conveyance system inside the confines of a well bore.

Perforating charge design innovations for cold production

As sand production became more and more desirable, the demand for larger and larger entrance hole diameter (EHD) became greater. When big hole (BH) charges were being introduced in the early 1980’s, the commonly used charges at the time had an EHD of 0.4" with a penetration (PEN) of 23". These BH charges typically had a maximum of .75" EHD and 14" PEN. A survey of heavy oil producers conducted in the early 1990’s asked how much penetration would they sacrifice in order to achieve a bigger EHD. The results of the survey was an acceptable minimum penetration of 12". An extra big hole (EBH) charge was developed that boasted of quality control (QC) specifications of 1" EHD and 10" PEN. It rapidly became the preferred charge for large numbers of heavy oil producers. This inspired the rest of the charge manufactures to follow suit. Figure 3 is a comparison table² of current heavy oil perforating products.

The pursuit of large and larger EHD is an attempt to prevent perforation plugging. Perforation plugging was, is and will be a major problem plaguing CP. The complex phase flow is very difficult to understand. Oil, sand, water and gas flow is complicated further with the presence of sand consolidation, ½" nodules, silt, clay, shale, scale and the ex-solution of gas. Perforation plugging therefore can not be predicted with simply sand to EHD ratios, or viscous drag and flow velocity.^{3   ii}  Further complications come when the blockage occurs in the formation. ⁱⁱⁱ

The nature of the jet charge design for larger EHD is very sensitive to the clearance between the casing wall and the carrier. Figure 4 shows this relationship. Casing size and weight, carrier size type and condition, the utilization of scallops and centralization; all have an effect on EHD. Even in more controlled conditions (i.e. API testing) there is quite a range of EHD. Figure 5. Each charge design has an unique character ( i.e. jet shape or the distance from the apex of the charge that the jet is fully formed) causing various effects to different charges. This also makes the modeling of EHD from one manufacture’s software to another manufacture’s charge impossible.