As Oil fields containing stacked reservoirs are developed, it is not uncommon for these reservoirs to be in pressure communication. The extent of pressure depletion may determine the viability of potential new drills. Possible communication of the X1 reservoir with the Y1 reservoir was initially suspected when a Material Balance study earlier conducted on the X1 reservoir did not yield a reliable historical pressure match using mapped volumes of the X1 thereby suggesting potentially larger Oil in Place number in the X1 reservoir. Also, the structural overlay of the X1 over the Y1 reservoir having compatible hydrocarbon contacts seemed to also indicate possible communication between the X1 and Y1 reservoirs. The conclusion of the Material Balance study recommended a more detailed probe into the X1 reservoir to ascertain the impact of communication on the reservoir development strategy. A simulation study was conducted primarily to evaluate the impact of communication uncertainty on the new drill recovery. Three scenarios were considered namely: Communication of the Y1 with the X1 through the aquifer; Communication of the Y1 with the X1 through the hydrocarbon and the Y1 completely isolated from the X1. The history match indicates reservoir communication through the aquifer as the most plausible scenario. However, due to active reservoir drive mechanism of gas Cap expansion and strong aquifer support in the X1 reservoir and possibly same in the Y1, all three scenarios did not adversely affect the potential recovery in this instance with recoveries between 50-59%. Hence incorporating surveillance information from offset producers is vital in evaluating production potential of zones which may be unproduced but not virgin.

The loss of drilling and completion fluids during well operations are not uncommon occurrences; the major challenge is the loss rate and duration of these events. Studies and experiences have shown that several factors contribute to loss events and are broadly classified into human and natural factors, and in most cases a combination of both. Agbami well operation is not an exception; while drilling well CZ46, an oil producer well in the Agbami field, severe losses in the magnitude of 350 bph was encountered. This happened while drilling the 12-1/4" hole section in the top part of the KMY reservoir. The solution to this loss circulation event is based on the a relatively simple well control principle; manage the reduction of the bottom hole pressure (BHP) to stop or drastically reduce losses without taking influx. Previous works provided a comprehensive description of the Agbami field and its reservoirs1,2. In line with conventional drilling engineering practices3,4,5,6 the choice of the mud weight was informed by pore pressure prognosis which was not accurately predicted in the case of this well. The losses were initially slowed down by intermittently pumping sized calcium carbonate and some other LCM pills; however, it soon became obvious that the pills will not cure the losses for wellbore drilling to continue. This event was happening at a time when the Deepwater Horizon/Macondo incident7 was still very fresh in the minds of most drilling folks especially those working in deepwater operations. The major pre-occupation for the drilling operations personnel on this well when the loss event happened was not to lose the primary means of well control which is the drilling mud hydrostatic pressure. The three main challenges that this loss rate posed were: how to reduce the loss rate in order not to run out of mud at surface; what lighter mud weight to displace the hole with; and how to carry out the displacement to a lighter mud weight. All the challenges must be resolved without taking influx or negatively impacting wellbore stability. The systematic method of displacement developed by the rig-site drilling operations personnel presented here was successfully implemented and has evolved to be called "Kill Line Base Fluid Displacement Method". The method can be adapted for use in severe loss circulation event in the deepwater environment and its success can be credited to treating the situation like a response to a well control event, although it is more of trying to avert one.

Time-lapse seismic survey also known as 4D seismic has established itself as a useful tool for reservoir monitoring and has gained wide acceptance within the industry. Technological advancements in the area of acquisition and processing have further strengthened the case for its application. The recent 4D seismic acquisition and interpretation in Agbami has proven to be an economically viable means of adding tremendous value to an oil field irrespective of the development stage it is in, and has been an excellent enabler for reservoir surveillance and resolution of subsurface uncertainties. Effective management of a field such as Agbami requires a surveillance method which can provide insight into spatial fluid movements with time, which the traditional surveillance methods are unable to provide. This type of insight is required to support sound reservoir management and field development decisions which Agbami 4D seismic provides. The information from the Agbami 4D monitor has shed more light around the fault network architecture within the field and has validated and in some cases changed some of the initial assumption around the sealing nature of these faults. Also, originally planned drilling locations and completion strategies have been modified based on the insight from the 4D seismic. The 4D seismic has also created value in the calibration of the reservoir simulation models and the location of bypassed oil within the field for future infill drilling. Forward modeling of expected seismic response based on proxy simulations helps to set realistic expectations of what can be seen in 4D seismic data. This paper discusses the acquisition, processing and interpretation of 4D seismic surveys in Agbami and how this information is being used to maximize the value in the field for the stakeholders.