When you start working on a film, you make your plans. First, there’s the script development, sharpening the screenplay, making sure that characters resonate and pop and are as colourful as they can be. Then there’s preparation, which usually means research, meeting with the people that inhabit the culture you are making the film about, and understanding all the peripheral players in that world. After I came aboard Deepwater Horizon, I jumped into the script, went down to Louisiana – and very quickly realised this was different. We were dealing with a culture of litigation.

Because the explosion and oil spill was so huge, that’s what dominated the area. You would go to these small towns in southern Louisiana, places you had never heard of, such as Port Fourchon, and you would see harbours full of boats with brand-new shiny engines, new trucks, people wearing brand-new Rolexes and new shoes. So many lawyers had moved in, there were so many lawsuits, and everyone who lived in that area had sued BP and made millions of dollars. They called them “spillionaires”. A lot of people got rich – some deserved it, some probably didn’t.

As we were making a movie about the spill, we were subject to the litigious psychology. BP became a very effective disruptor and prevented us getting any access to any oil rigs. We couldn’t even fly by one. At one point we were in a helicopter on a tour of a rig called the Nautilus and were told if we got any closer we would be perceived to be a threat and they were going to defend themselves. The companies exert so much power because they are such financial engines in that part of the country – anyone who worked with BP basically said they couldn’t talk to us. We had consultants who would work with us for a day or two, but the third day they would call in sick and we would never hear from them again. We had contracts to film on the tenders that go back and forth to the rigs – then the day before, they would say we couldn’t. It became obvious that BP was doing a great job of intimidating most of the people down in that community. We understood it; it wasn’t a news flash. BP pays a lot of bills there, a lot of mortgages, sends a lot of kids to school, pays a lot of medical insurance. We realised our only option was to build our own rig – which we did.

We also found that several of the people who were involved in the real-life incident clearly had gag orders as a result of their settlement with BP; they told us they could not speak with us. The ones who did not have gag orders did speak to us. BP’s two main rig supervisors, Donald Vidrine and Robert Kaluza (who were played by John Malkovich and Brad Leland), did not speak to us. But because their testimony from the congressional and coastguard hearings is on record, we were able to capture so much of their documented actions and conversations that we didn’t really need to speak to them.

The legal processes were something else. Lionsgate, our studio, had a team of independent lawyers who would review every word in the script, constantly. It didn’t stop there: because I do a lot of improvisation, things change during the shoot. So in the final edits the lawyers were all over me; it was the first time in my career I have ever had to take mandatory edits from the studio. For example, we had a scene that might have suggested that workers were under pressure to say the rig was safe because BP managers wanted to move on to another oil well. It was 100% true and very well documented, but the lawyers were concerned it was making BP look too responsible for the blowout. So we had to back off. It was frustrating.

We were also being closely monitored as to how we portrayed the actual events. If you asked 50 experts why the Deepwater oil rig blew up, you will get 50 different answers. Clearly, it was a confluence of events, not one single thing; but the one area pretty much everyone agrees on was the issue with the cement pour at the bottom of the well. They put it down in order to control the pressure of the well, and before it can be proclaimed safe they should do an inspection called a cement bond log. It’s basically sending sonar signals down to make sure there are no hollow spots. BP sent the team home; they never did the test. That’s fact, very well documented, and most people believe it was the beginning of the problem.

It’s very likely BP either wanted to save the $125,000 (£98,000) it would have cost – or, as my feeling is, they didn’t want to know. If there was a problem they would have had to pull up all the cement and redo the job, which could take another three weeks at $1m a day. The lawyers’ argument was: if you say the cement bond was cracked, the subcontractor who made the bonding solution will sue, and we can’t prove the solution was faulty. If you say the test wasn’t done, the company that was sent home will say that’s slander. That was where we really dug in. It sounds trivial, but we argued for a week about how much we could say the cement pour was the catalyst that led to the blowout.

The thing to remember is that BP don’t own the rigs, they rent them. The way the rigs are organised, and the way the different companies work together, is fascinating. It’s a complex social organisation of subcontractors, who have different jobs on the rig at a given time. For example, Transocean own the rig. Schlumberger were expecting to do the cement bond log.

One small surprise: we were able to use actual BP logos in the film. It’s one of those things where you scratch your head with the lawyers. Normally we’re told we have to modify logos – but they are public domain, and to capture them on film is not illegal.

What was behind it all was litigation insurance, to protect the studio from legal action. All the lawyers I was dealing with were themselves dealing with lawyers from the insurance company. As far as Lionsgate were concerned, any issue that was going to preclude the insurance bond from closing was non-negotiable. I was having to edit my film based on an insurance company, and that was crazy. BP may very well sue, but we believe we have defensible positions.

At the end of the day, we might be the best thing that could happen for BP. Nobody thought the cement pour would have led to what it did. Vidrine and Kaluza were wrong, but there was no criminal intent there. We are clear on that. BP behaved as a company for profit, which it is – but we all participate in capitalist society. Every time we drive a car or fly in an airplane, we are all complicit in this relationship. BP isn’t some great devil forcing us to live these lifestyles. BP had many problems drilling that well that certainly weren’t all BP’s fault – that was why it was called “the well from hell”. I think we made BP look reasonable in its reactions to events. That’s not to say its two guys weren’t on the rig; they were in charge, and made some big mistakes. If anyone had really understood that something this bad was going to happen, they would have stopped it for sure; no one realised what the price could be for the shortcuts. I’ll bet you BP are not going to be so quick to cut corners in future.