Due Diligence.  An operator must have a reasonable idea of basic blowout hazards associated with a given field or planned drilling activity, and likely consequences, where he operates. This hazard assessment is generally going to be subjective as industry statistics on blowout incidents are generally unreliable due to small sample size and the large number of independent variables associated with each. The assessment should be documented, with appropriate logic to back up the opinion.

Based on this initial judgment, an operator will decide whether additional detailed hazard assessment and control evaluation is warranted beyond acceptable standard operating/design practices. If justified, hazard analysis expansion should be continued until cost effectiveness based on total field investment and potential liability begins to diminish.

• Human Impact: Wells with: lethal H₂S concentrations, manned offshore jackup or platform, near population center, highly explosive HPHT gas condensate, hostile environments, remote.
• Environmental Impact: Environmentally sensitive areas with highly productive oil reservoirs, H₂S.
• Asset impact: Offshore platforms, loss of high cost well(s), large loss of hydrocarbons.
• Business disruptions: Reallocation of resources (human and material), domino business disruptions, loss of sales, contract problems, litigation, drop in stock value, cash flow disruptions.
• Public Image Impact: Human causalities, real or perceived environmental damage, wild life casualties, real or perceived public safety concern, public disruption (evacuations, closed roads, railroads, air traffic), local government problems (particularly in foreign countries), real or perceived liability claims.

• Any high GOR well(s) with high open flow potential (IPR). Risk increases with pressure, temperature, corrosive gases (H₂S, CO₂), low kick tolerance and loss zones.
• Abnormal pressure. Risk increases with rapid transition zones, low kick tolerance, loss zones above reservoirs, high deliverability reservoirs (kh).
• Normal pressured high deliverability gas zones behind intermediate casings. Highest risk of flow behind casing during cementing and waiting on cement.
• Areas where simultaneous activities are being implemented (e.g., drilling and production).
• Areas where crews have minimal experience, communication is complicated by national crews and supervision is stretched.
• Foreign areas where resources are limited, logistics are complicated, maintenance and well construction is marginal.
• Exploration areas where formations and reservoirs are unknown.
• Areas where new operations are attempted with limited experience, requiring steep learning curve: e.g., deep water, multi-lateral drains, coil tubing drilling and completions, horizontal, under-balance drilling or combinations.
  
  Example Situations Where Quickly Executing a Relief Well May be Difficult