Matrix Acidizing Design and Quality- Control Techniques Prove Successful in Main Pass Area Sandstone (includes associated papers 17274 and 17466 )
- Dan H. Brannon (Conoco Inc.) | Collete K. Netters (Conoco Inc.) | Paul J. Grimmer (Conoco Inc.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- August 1987
- Document Type
- Journal Paper
- 931 - 942
- 1987. Society of Petroleum Engineers
- 4.1.5 Processing Equipment, 2.2.2 Perforating, 3.2.4 Acidising, 5.2 Reservoir Fluid Dynamics, 5.1.1 Exploration, Development, Structural Geology, 3 Production and Well Operations, 5.6.9 Production Forecasting, 3.4.1 Inhibition and Remediation of Hydrates, Scale, Paraffin / Wax and Asphaltene, 1.10 Drilling Equipment, 4.6 Natural Gas, 4.2.3 Materials and Corrosion, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 1.8 Formation Damage, 4.3.3 Aspaltenes, 2.7.1 Completion Fluids, 2.5.2 Fracturing Materials (Fluids, Proppant), 2.4.5 Gravel pack design & evaluation, 4.3.4 Scale, 6.5.5 Oil and Chemical Spills, 1.6 Drilling Operations, 5.6.3 Pressure Transient Testing, 4.1.2 Separation and Treating, 3.1.6 Gas Lift, 2 Well Completion, 2.5.1 Fracture design and containment, 2.4.3 Sand/Solids Control
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Summary. Successful acidizing techniques have been developed and implemented in the Main Pass area, offshore Louisiana. Since mid-1984, 37 oil wells have been acidized. resulting in a success rate of 95% and a total increase in production of almost 12,700 BOPD [2019 m3/d oil].
One of the primary reasons these treatments were so successful was the continuous injection of a finely ground oil-soluble resin diverting agent throughout all acid stages, which decreased acid injection into the more permeable zones and helped distribute the treating fluids more uniformly.
Other factors that may not be the industry norm that influenced the effectiveness of these treatments included (1) reduced-strength HCl/HF and preflush acids, (2) xylene solvents pumped ahead of injected acid for preflush acids, (2) xylene solvents pumped ahead of injected acid for possible paraffin and/or asphaltene removal, (3) xylene pumped after the possible paraffin and/or asphaltene removal, (3) xylene pumped after the overflush stage as a diverter breaker, (4) filtration of all fluids, (5) low-rate, high-pressure pump for continuous injection of diverter downstream of filters, (6) use of "pickled" coiled tubing, (7) coil/ production tubing annulus pressure recorder, (8) testing production tubing production tubing annulus pressure recorder, (8) testing production tubing before pumping, (9) use of boats exclusively, rather than offloaded skids, from which to mix and pump, (10) on-site acid mixing with titration checks of concentration before pumping, and (11) postjob laboratory analysis of concentrations and solids content of selected spot samples.
The Main Pass wells acidized are located offshore Louisiana in Blocks 288, 296, and 311, about 30 miles [48 km] east of the mouth of the Mississippi River. Thirteen different sands, which range in depth from 4,500 to 6,500 ft [1372 to 1981 m], have been acidized to date. The native permeabilities of these formations range from 100 to 1,000 md. Other average reservoir parameters include 27% porosity, 25% water saturation, and 140 degrees F [60 degrees C] formation temperatures. Perforated intervals range from 12 to 110 ft [4 to 34 m], and the majority of the wells are dually completed.
Of the wells acidized in this program, when completed, 51 % were perforated overbalanced with 16 shots/ft [52 shots/m] followed by perforation washing. The other 49% were perforated with 12 shots/ft [39 shots/m] with various degrees of underbalance. All completions were gravel-packed for sand control, and all completion fluid was filtered. Both types of completions produced some wells with high degrees of skin damage.
The formations acidized contain low quartz, high clay minerals, high feldspar, iron minerals, and low-API-gravity crudes (15 to 28 degrees API [0.97 to 0.89 g/cm3]), which are undesirable characteristics in sandstone acid candidates. This rock composition, combined with sand-control installations and completion fluid, is often susceptible to impairment, which can be chemical (such as clay damage) or mechanical (such as particulate plugging caused by entrained solids in the completion fluid) in nature.
Skin damage is a major reason many Main Pass wells do not reach their production potential. Determining whether the major cause of damage is drilling, perforating, gravel packing, or migrating fines is very difficult, perforating, gravel packing, or migrating fines is very difficult, however, each of these probably contributes to some extent. This acidizing technique was designed to increase or to restore permeability into the wellbore with a minimum disturbance of the stabilized wellbore inflow framework by reducing skin.
Few solid correlations were found between success (i.e., skin reduction) and any one of the new techniques performed because so many techniques were changed at performed because so many techniques were changed at once that no single item could be independently tested. Because we think that each new technique has theoretical and practical merits, we were reluctant to reduce the effectiveness of the job by omitting one or more for the sake of science.
Our data base is relatively small and confined to a relatively narrow, type of formation, but the techniques presented are sound. and most are applicable to all presented are sound. and most are applicable to all sandstone acidizing.
Since the installation of our first Main Pass platform in 1970. acid stimulation has been used to restore and maintain production rates from wells in decline. Three distinct acidizing periods that contributed to the evolution of our current design were experienced: pre- 1978, 1978-81, and 1982-84. These periods are evidence of advancing technology in the industry. as well as changing management philosophy.
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