When performing hydraulic fracturing treatments, the completion community widely recognizes that if the perforations can be oriented to the maximum principle stress plane and the shot density can be maximized accordingly, the success of the fracture treatment will be much greater. These benefits result from the lower breakdown pressure and the minimal tortuosity effects experienced during the process when the above conditions are met. Also, if the perforations are oriented in the maximum principle stress plane for a naturally completed, cased, and perforated well, the resulting perforation tunnels will usually be more stable than other perforations that are placed away from this preferred stress plane.
In natural completion scenarios, oriented perforating becomes especially important if 1) the formation integrity is questioned, and 2) sustained production without the mobilization of sand that could impact production is challenged. Normally, when faced with this dilemma, operators have automatically defaulted to a conventional sand-control treatment to ensure that production is not interrupted and that costly well interventions to clean out wellbore sand accumulation will not be required. While traditional sand control methods; i.e., installation of screens, proppants, and completion fluids used in the completion, are capable of controlling unwanted sand production; significant productivity penalties are often experienced with their use.
Now, there is another viable sand-control option that can be considered by the industry. If the completion is a candidate for sand management, a gravity-force-oriented perforating strategy, which will eliminate traditional sand control treatments, can be planned. Since the system relies on gravity for proper orientation, the most important consideration for using this concept is that the wellbore under consideration must have a minimum deviation of 25 degrees to orient to maximum principle stress or the overburden gradient.
The new perforating system was used in a North-Sea field and resulted in a 37,600 BOPD sand-free production rate. The new gun system can be conveyed on wireline or coiled tubing and can also be used in conventional tubing-conveyed perforating (TCP) applications.
The relationship between geomechanics and completion optimization has been studied extensively and well documented in the literature.1 For a vertical completion, it is advantageous to define the minimum and maximum horizontal stresses and orient the perforations to the maximum horizontal stress to improve the hydraulic fracturing treatments and increase the probability of more stable perforation tunnels for a "perforated only" completion. Generally, when designing the perforation strategy for a cased horizontal completion, the dominant stress field will be the vertical or overburden gradient. Therefore, it is important that the perforations in the horizontal completion be directed to the top and bottom (180° phasing) of the wellbore to the maximum stress field. Modeling tools are available to assess well productivity associated with perforating with higher-shot-density, spiral-phased gun systems versus reduced shot density at 180° phase. It is very important to evaluate the differences in well productivity that can occur when selecting an oriented perforating strategy and select the perforating strategy that will maximize reservoir recovery.
After the decision has been made to adopt an oriented perforation strategy, the design of the program must be designed to assure that the perforations are accurately placed in the proper stress orientation. Minor errors in perforation placement can lead to inefficiency in initiating hydraulic fractures and perforation tunnel collapse or production of sand with a natural completion. Diagnostic tools are readily available during the drilling phase to determine the state of stress in the near wellbore region (as described by Brudy2); however, the perforating hardware and accessories required to position the perforation planes have been less than reliable.