A new approach to workovers using large-amplitude excitation of the wellbore fluid has proven successfir in establishing or restoring well productivity in Cold Heavy Oil Production (CHOP) wells in Alberta and Saskatchewan. The workover Qpically takes from five to 12 hours, and involves large amplitude pressure pulses achieved by sudden stroking of a downhole piston. A great deal of strain energy is input to the reservoir by the aggressive stroking, and this unblocks the near-wellbore, loosens and liquefies the unconsolidated formation, and even affects the interwell region, where stable large-scale sand arching can be perturbed so that sand production can recommence. A fluid such as dead oil from the same field, can be simultaneously introduced during pulsing, or it can proceed without net fluid addition.
The method has proven useful as a means of bring a well onto reasonable production by initiating sand influx where other methods have failed. It is different than swabbing, which may reconsolidate the unconsolidated sand. Pressure pulsing instead pushes the sand vigorously away from the perforations with an aggressive liquid pulse, and this leads to permanent porosil), perturbations. These perturbations, which propagate gradually out into the reservoir, loosen precipitated asphaltenes and fines, as well as loosening the sand, so that when the well is placed back on production, a disturbed zone that is sufficiently large to lead to continuous sanding is generated. In several cases, wells that had never produced more than I m3/d because of a failure to initiate sand injlux were converted into reasonable CHOP wells (4–8 m3/d).
In a number of cases, pressure pulsing has even reconnected the wellbore to high pressures that existed in the far field. The mechanisms are relatively well understood, as a theoretical model exists to explain them. In practical terms, we Us generally become better producers, and the method can also be applied to conventional well workovers in all cases where mechanical skin exists or chemicals are to be placed.
Although it is generally applicable to any case of mechanical blockage or chemical placement, the PE-TECH Pulse Enhancement TECHnique) workover approach was initially developed for oil wells that use the method of Cold Heavy Oil Productionl,2 (CHOP). It has been applied in 30 cases in 9 different fields since the first experimental trials in June 1998 in Alberta and Saskatchewan (Table 1). A reasonable success ratio has been given the developmental nature of initial efforts and because many of the initial candidates were generally wells that we now consider poor candidates through our rigorous selection criteria.
The PE-TECH workover method is beneficial in wells where production cannot be initiated by standard well completion methods, where mechanical blockage (fines, asphaltenes, perforation plugging) and near wellbore damage due to drilling mud or cement invasion inhibit flow into the wellbore. As well, given that pressure pulsing promotes fluid dispersion rather than fmgering, the PE-TECH workover method is the best technique to introduce a chemical in a uniform, well-dispersed manner into a reservoir.