>If I execute this SQL, I obtain 2493 records:
>
>

>DECLARE @GeographyCoordinate Geography
>DECLARE @Area Geography
>
>SET @GeographyCoordinate=Geography::Point(47.79208,-65.71996,4326)
>SET @Area=@GeographyCoordinate.STBuffer(9931*1000)
>
>SELECT Company.PrimaryKey,@GeographyCoordinate.STDistance(Geography)/1000 AS Distance 
>FROM Company 
>WHERE @Area.STIntersects(Company.Geography)=1
>

>
>However, if I add one kilometer:
>
>

>DECLARE @GeographyCoordinate Geography
>DECLARE @Area Geography
>
>SET @GeographyCoordinate=Geography::Point(47.79208,-65.71996,4326)
>SET @Area=@GeographyCoordinate.STBuffer(9932*1000)
>
>SELECT Company.PrimaryKey,@GeographyCoordinate.STDistance(Geography)/1000 AS Distance 
>FROM Company 
>WHERE @Area.STIntersects(Company.Geography)=1
>

>
>...it cannot find any more record.
>
>Is this a limit of the buffer?


From BOL:

STBuffer (geography Data Type)

distance
Is a value of type float (double in the .NET Framework) specifying the distance from the geography instance around
which to calculate the buffer.

The maximum distance of the buffer cannot exceed 0.999 * π * minorAxis * minorAxis / majorAxis (~0.999 * 1/2 Earth’s
circumference) or the full globe.


So, maybe 9931*1000 exceed max distance, becuase

DECLARE @GeographyCoordinate Geography
DECLARE @Area Geography

SET @GeographyCoordinate=Geography::Point(47.79208,-65.71996,4326)
SET @Area=@GeographyCoordinate.STBuffer(9931*1000)

SELECT @Area

shows NULL as a result.