![]() ![]() If the formation of interest has gravel-pack completions in nearby fields, rely on these. In this event, rely on any of the samples from offset wells. If available, small plugs can be taken under controlled circumstances at various sections of the core for a complete and accurate median formation grain size and grain-size distribution determination.įrom time to time, operators have no formation sample. Coring in sand-producing formations is also plagued with poor recovery. Although conventional cores are the most desirable formation sample, they are not readily available in many wells because of the cost of coring operations. In the case of unconsolidated formations, rubber sleeve conventional cores may be required to assure sample recovery. The most representative formation sample is obtained from conventional cores. Experienced lab analysts can separate the effects of crushing and mud solids prior to evaluating the sample, thus improving the quality of the results. The core sample also contains drilling mud solids that can be mistaken for formation material. When the projectiles strike the face of the formation, localized crushing of the sand grains occurs, producing broken sand grains and generating more fine particles. Although more representative than produced or bailed samples, sidewall core samples can also give imprecise results because the volume in each sidewall sample is small. ![]() Taking sidewall core samples is generally included in the evaluation stages of wells in unconsolidated formations these are the most widely used sample types for gravel-pack sand design. The projectiles remain attached to the gun with steel cables, so that when the gun is pulled from the well, the projectiles are retrieved with a small formation sample inside. Sidewall core samples are obtained by shooting hollow projectiles from a gun lowered into the well on an electric line to the desired depth. The use of bailed samples may result in the design of larger than required gravel-pack sand that can result in sand production (small formation particles passing through the gravel pack) or plugging of the gravel pack (small formation particles filling the spaces between the gravel-pack sand grains). This results in a sorting of the formation sand grains into a sample that is not representative the formation sand. When closing the well in to obtain a sample, the larger sand grains settle to the bottom of the well first, and the smaller sand grains fall on top of the larger ones. Bailed samples also may be misleading in terms of grain size distribution. Bailed samples are generally biased to the larger-size sand grains, assuming that more of the smaller grains are produced to surface. Samples collected from the bottom of a well using wireline bailers are also relatively easy to obtain, but these too are probably unrepresentative of the size of the actual formation sand. Also, the transport of sand grains, through the production tubing and surface flow lines, may result in broken sand grains, causing the presence of more fine and smaller grains. This is the reason that the surface sample is not a good representation of the various sizes of formation sand. In many cases, the larger sand grains settle, so a sample that is produced to the surface has a higher proportion of the smaller-size sand grains. The well’s flow rate, produced fluid characteristics, and completion tubular design influence whether a particular size is produced to surface or settles to the bottom of the well. Although such a sample can be analyzed and used for the gravel-pack sand size determination, produced samples will probably have a smaller median grain size than the median of actual formation sand. With knowledge of the different sampling techniques, compensation can be made in the gravel-pack sand size selection, if necessary.Ī produced sample of the formation sand is easily contaminated before it reaches the surface. Because the formation sand size is so important, the technique used to obtain a formation sample requires attention. ![]() Failure to analyze a representative sample can lead to gravel packs that fail because of plugging or the production of sand. ![]() The first step in gravel-pack design is to obtain a representative sample of the formation. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |