Monitoring Areal And Vertical Sweep And Reservoir Pressure In The Ghawar Field Using Multiprobe Wireline Formation Tester

Abstract

Saudi Aramco's Ghawar Field is a massive carbonate reservoir with sub-zones of varying reservoir quality and has been under flank-water injection. It is a complex reservoir, with thin super permeability layers (10 feet) that are generally stratiform and in some cases fractured, associated with high productivity. Laterally extensive super permeability beds, in good vertical communication with the rest of the oil bearing reservoir, can significantly increase both well productivity and sweep efficiency. However, isolated super permeability layers can cause early water breakthrough, which adversely affects oil recovery as well as increases the field operational cost. Furthermore, large permeability contrasts can complicate effective drainage of lower porosity zones in the lower part of the reservoir that contains about 35 % of the original oil in place. For this field, pressure and saturation monitoring have been key factors in achieving the overall reservoir management objective of maximizing recovery at the lowest cost. Saudi Aramco is currently surveying the key new wells drilled behind the flood front using the multi-probe formation tester for obtaining pressure measurements, performing interval tests, and taking fluid samples along the well-bore. The primary objective of the surveys is to establish whether the super permeability beds as well as the lower porosity zones are introducing differential pressure depletion, which will directly impact the field's completion and production strategy. Obtaining fluid samples across the reservoir zones is also a key part of the surveys, to establish water salinity and movable oil fraction in zones with breakthrough where the injection and formation waters are mixed. Determining the fraction of movable oil in the lower porosity zones, where the conventional open-hole log results are uncertain, is very crucial in optimizing recovery. It is also a powerful method to evaluate the sweep in the lower zones matrix where the diffused fractures density is higher and assist the dynamic interaction between the two systems. The on-going Uhawar Field monitoring has shown that there is good vertical communication in the higher quality zones, at the top of the reservoir and embody the super- permeability thin beds. However, local and reservoir scale barriers as well as differential depletion has been observed towards the base of the reservoir. These barriers have resulted in poor sweep efficiency with zones containing bypassed oil. These zones are now being targeted by dedicated dual vertical-horizontal completions. In this paper, we show that the pressure and saturation monitoring integrated with other dynamic and geological data contribute immensely to obtain the best completion for optimizing oil production and recovery. Furthermore, we also show that in areas of good vertical communication, super permeability is advantageous to the field development, due to its high productivity and large drainage area exposure. P. 111

An Integrated Efficient Approach To Perform IPTT Interpretation

“…There are a number of papers that discuss building reservoir models using borehole images and openhole logs [1][2][3][4][5][6][7][8][9] [13] . An iterative regression strategy for multiple IPTTs was also introduced in literatures [5][11] [18] .…”

“…Borehole Images (such as resistivity, sonic, LWD density images, etc) And Local Knowledge A number of papers had descriptions how to use static information such as openhole logs and borehole images to define the layering or reservoir model [1][2][3][4][5][6][7][8][9] [13] . The following sections of this paper will concentrate on the importance of dynamical data and how to use them to refine and confirm the most probable layering or reservoir model when the initial reservoir model is defined according to static information.…”

“…If core samples are taken frequently, says every 1ft, then, the average Kv and Kh of permeable layers may be computed, usually using arithmetic and harmonic averaging. A number of papers had comparisons between MDT* pretest mobilities/permeabilities and core permeabilities [1][2][3][4][5][8-11] [13] . Comparing with core measurement, the volume of investigation of MDT* pretest is larger than that of a core plug, but of the same order of magnitude generally (figure 1) [5] .…”

“…Interval pressure transient testing (IPTT) with an advanced formation tester MDT* has been widely applied to measure permeability and permeability anisotropy [1][2][3][4][5] [9][10] [14] . IPTT also has been used for other applications, such as to perform sweep efficiency monitoring of gas injection [3] , formation characterization in retrograde gas fields [6] , characterization of fractures and faults [7] , and so on.…”

“…IPTT also has been used for other applications, such as to perform sweep efficiency monitoring of gas injection [3] , formation characterization in retrograde gas fields [6] , characterization of fractures and faults [7] , and so on. IPTT involves the simultaneous measurement of pressure transients at various locations along the length of the MDT* tool.…”