Lost circulation events are a common phenomenon in the oil and gas industry and there are numerous service providers that offer a wide range of different LCM products to manage fluid losses when drilling oil or gas wells. However, if none of these products are able to bring the desired success it might be required to step away from conventional techniques and products in order to be successful. Engineers are then challenged to think outside the box in order to come up with a solution. The prime purpose of this thesis is to develop a method that can successfully combat the lost circulation events which were expected to be encountered during the second phase of OMV’s Maari Growth Drilling Campaign in New Zealand. In order to achieve the mentioned target, the thesis was divided into three parts. The focus in the first part is on the technical challenges during the planning phase of the Maari drilling campaign as well as during execution. The campaign was planned to further develop the Maari field. Throughout the planning phase measures to combat lost circulation were prepared to a high level of detail. However, the high degree of depletion that was actually encountered in the reservoir was unexpected. Further the reservoir was found to be heavily faulted. Due to the horizontal geometry of the wellbore in the reservoir section placing LCM effectively was found to be nearly impossible. The challenge was to find a way to seal off the loss zone without compromising the reservoir permeability. The purpose of second part in this thesis is to investigate the different fluid loss events that were encountered during the first phase of the campaign. The fluid loss events while drilling horizontal reservoir sections and the measures undertaken are looked at in detail. When the wells were drilled fluid losses occurred very early in the reservoir section. At the beginning and according to the planned procedure conventional LCM pills of different composition and volume were pumped. Rather quickly it turned out that the treatments remained unsuccessful and cement plugs had to be set in the open hole. Due to the high inclination of the wellbore it was not possible to keep the cement in its designated position without taking the risk of cementing in the string. The third part of the thesis presents available options for fighting against lost circulation in horizontal wellbores. Different products and methods were examined and their practical applicability was discussed thoroughly. One method, which was considered as the most promising way to success, was given a try during operations. It turned out to be the right decision. The technique of squeezing foam cement into the loss zone using an open hole packer without compromising the reservoir was perfected through the campaign. The development with all its lessons learnt is discussed in this thesis. Eventually a method was developed that can prevent from using up a contingency string and losing a hole size in the reservoir.